The expansion of HIV/AIDS care and treatment in resource-constrained countries, especially in sub-Saharan Africa, has generally developed in a top-down manner. Further expansion will involve primary health centers where human and other resources are limited. This article describes the World Health Organization/President's Emergency Plan for AIDS Relief collaboration formed to help scale up HIV services in primary health centers in high-prevalence, resource-constrained settings. It reviews the contents of the Operations Manual developed, with emphasis on the Laboratory Services chapter, which discusses essential laboratory services, both at the center and the district hospital level, laboratory safety, laboratory testing, specimen transport, how to set up a laboratory, human resources, equipment maintenance, training materials, and references. The chapter provides specific information on essential tests and generic job aids for them. It also includes annexes containing a list of laboratory supplies for the health center and sample forms.