The Rocky Flats Beryllium Health Surveillance Program (BHSP), initiated in June 1991, was designed to provide medical surveillance for current and former employees exposed to beryllium. The BHSP identifies individuals who have developed beryllium sensitivity using the beryllium lymphocyte proliferation test (BeLPT). A detailed medical evaluation to determine the prevalence of chronic beryllium disease (CBD) is offered to individuals identified as beryllium sensitized or to those who have chest X-ray changes suggestive of CBD. The BHSP has identified 27 cases of CBD and another 74 cases of beryllium sensitization out of 4268 individuals tested. The distribution of BeLPT values for normal, sensitized, and CBD-identified individuals is described. Based on the information collected during the first 3 1/3 years of the BHSP, the BeLPT is the most effective means for the early identification of beryllium-sensitized individuals and to identify individuals who may have CBD. The need for BeLPT retesting is demonstrated through the identification of beryllium sensitization in individuals who previously tested normal. Posterior/anterior chest X-rays were not effective in the identification of CBD.