Chronic beryllium disease (CBD) diagnosis hinges on demonstrating a cell-mediated immune response to beryllium salts in vitro with the beryllium lymphocyte proliferation test (BeLPT). The BeLPT has found widespread application in screening for CBD and beryllium sensitization in populations of exposed workers. We hypothesized that the in vivo beryllium salt patch test may be of value as an adjunct to the BeLPT, rectifying false negative or ambiguous blood test results. We studied subjects with CBD (n = 11), beryllium sensitization without disease (n = 3), and control subjects with dermatitis (n = 20). Evaluation included completion of a demographic questionnaire, blood BeLPT (if CBD or beryllium-sensitized), and beryllium patch testing with 0.1% and 1% beryllium sulfate (BeSO4) in petrolatum and in aqueous vehicles. Biopsies were performed at abnormal patch test sites in five subjects. The 1% aqueous BeSO4proved superior either to 1% petrolatum or 0.1% solutions, producing positive reactions in all CBD and beryllium-sensitized subjects. We observed no long-term adverse reactions. Biopsies demonstrated spongiotic changes early, followed by noncaseating granulomas within 18 days. We conclude that the beryllium patch test can be used safely to clarify the sensitization state and diagnosis of CBD.