I studied a network of small forested areas (2-2744 ha) that are protected as forestry research control sites and nature reserves in Peninsular Malaysia. These areas are officially known in Malaysia as Virgin Jungle Reserves (VJRs). They are unlogged and are usually part of a larger generally logged forest. I examined the effects of habitat disturbance on the species richness and composition of the mammal communities in seven of these protected areas (70-304 ha) and in adjoining logged forest, exotic monoculture plantation, or "farm bush." Thirty-eight species of mammals were recorded through direct observation, identification of tracks or other signs. The size of the remaining area of natural forest, Including both logged and unlogged forest but not including exotic timber plantations, or farm bush, was the most important factor affecting the mammal communities in all seven areas. The presence of species followed a nested subset pattern A loss of large herbivores and carnivores in particular, was apparent between areas of natural forest of 6551 to greater than or equal to 10,000 ha. When areas of natural forest of less than or equal to 459 ha were considered, size continued to be critical; a sharp loss in mammal species richness was apparent between 70 and 164 ha. The area of the natural forest in which a protected area was located largely determined the mammal species richness and composition in the protected area. Differences in habitat quality accounted for the differences in mammal communities between Protected areas and their adjoining vegetation. The preservation of small undisturbed areas can effectively enhance certain mammal communities in a disturbed landscape. The survival of some mammal species, how ever, including the largest carnivores and herbivores, will be determined by the area of surviving forest as a whole. A positive management strategy would be to retain large, continuous al-eas of forest wherever possible, in Preference to fragmenting forest, and to build on existing small protected-area networks such as the VJR network in Peninsular Malaysia, so that logged forests contain a rich mix of undisturbed protected areas.