Our objective was to determine the yield and cost of standardized laboratory testing of HIV-infected patients entering medical care after testing positive for HIV. An HIV staging and referral clinic in a municipal public hospital was our site for a cross-sectional study, and 308 patients were evaluated in the clinic between February 1, 1990 and October 1, 1991. Patients underwent standardized laboratory testing, including hematologic studies, serum chemistries, infectious disease serologies, and chest radiographs. The percentage of abnormal results for each test was determined. Abnormal results were stratified as mild or severe. They were also examined with regard to whether injection drug users or other patient subgroups had higher percentages of abnormalities. Changes and Medicare reimbursements for the tests were also determined. There were substantial numbers of abnormalities in all types of laboratory testing. Only 3% of patients had normal CD4 lymphocyte counts; 85% had counts of < 500/mm3, and 35% were < 200/mm3. Forty-four percent of patients had at least one abnormal hematologic study; 8% were severe. Nearly 75% had abnormal liver function tests; 20% of these were severe abnormalities. Fifteen percent of patients were PPD-positive, and > 50% were anergic. Fourteen percent had a positive nonspecific test for syphilis, and 7% had a positive confirmatory test. Fourteen percent of patients had an abnormal chest radiograph.(ABSTRACT TRUNCATED AT 250 WORDS)