In the early 1970s, the provinces of Southern Tagalog Region (comprising Aurora , Batangas, Cavite , Laguna, Marinduque, Mindoro, Palawan, Quezon, Rizal and Romblon) was formerly merged with Region 3 ( Central Luzon ). In 1976, these provinces formed a part of a newly created region known as Region 4 ; hence, a new Regional Health Office – RHO 4 was created under the directorship of Regional Director Edilberto G. Fernando. He was then succeeded by Director Jose R. Ybanez in 1980.
In 1982, in line with the reorganization of the Ministry of Health (MOH) under Executive Order No. 851 integrating the preventive, promotive, curative and rehabilitative services; organizational and functional changes have transpired. With the reorganization, Regional Health Office was renamed the Regional Health Services (RHS) (headed by the Regional Director) who has the administrative authority over the Provincial Health Officers, City Health Officers, District Hospital Chiefs and Municipal Health Officers. At the provincial level, both the public and hospital services were put under the administration of the Provincial Health Officer; while for the district level; the Chief of the District Hospital administered both the district hospital and Rural Health Units within its catchment area (RHUs were previously under the supervision of the Provincial Health Officer).
People power of 1986 saw another reorganization in the government –– streamlining the bureaucracy. With the issuance of Executive Order No. 199 in 1987 , the 5 th re-organization took place, renaming the Ministry of Health into Department of Health (DOH) and Regional Health Offices into DOH - Integrated Regional Field Office (DIRFO) . About 30% of health personnel from Regional Offices were transferred to the field offices – Provincial / City Health Offices and Hospitals.
The passage of Local Government Code in 1991 paved the way for a decentralized bureaucracy in the country in which health service facilities such as the Provincial / City Health Offices, Hospitals, Rural Health Units and Barangay Health Stations were devolved to the local government units. In the light of this devolution, only Regional Health Offices and Specialty Hospitals and Services were retained under the DOH administration. In Region 4, only 3 specialty hospitals were retained under the RHO4 management, namely: Culion Sanitarium (Palawan), J.N. Rodriguez Memorial Hospital (Tala, Caloocan ) and Batangas Regional Hospital (Batangas). In the late 1990s, Regional Extension Offices (REOs) were established in the different provinces of the region headed by the Provincial Health Team Leader. These REOs provided the link between DOH-RHO4 and the local government units.
At the turn of the new millennium (year 2000), the DOH experienced further streamlining with the implementation of Executive Order No. 102 redirecting its functions and operations in view of the devolution of basic service delivery to the local government. Regional Health Offices were renamed Centers for Health Development (CHDs) with functions focused on policy development, regulations and licensing enforcement, provision of technical and logistic assistance (including advocacy, monitoring and evaluation); and resource management. To perform these new mandates, CHDs has undergone re-engineering in its organizational structures as follows: 2 new divisions were created to administer the regulations / licensing enforcement and local health assistance functions of the agency; the administrative and finance divisions formerly working as separate offices were merged into one division - named as Management Support Service Division.
By 2003, another major re-organization was experienced by CHDs particularly the Southern Tagalog Region pursuant to Executive Order No. 103 . With an original wide area coverage of 11 provinces and 10 cities, Region 4 was divided into 2 sub-regions, namely: Region 4A (covering the 5 CaLaBaRZon mainland provinces of Cavite , Laguna, Batangas, Rizal and Quezon); and Region 4B (comprising the 5 MiMaRoPa island provinces of Occidental and Oriental Mindoro, Marinduque, Romblon and Palawan ). Aurora province which was formerly part of Region 4 was now transferred to Region 3 (Central Luzon Region). This downsizing of CHD 4 into CHD 4A and 4B was a big and critical step of President Macapagal administration to ensure the efficient and effective delivery of its redirected functions and health services to the people in the region.