Biochemical evaluation of calcium stone patients: how soon can it be done after stone surgery/passage? Biochemical evaluations were done two times for 29 outpatients with calcium stone disease, the first time within one month after surgical extraction or passage of stones and the second time two months or more later. Classification of the etiologic basis for the stone disease was the same after both tests in 27 patients. In the other 2 patients the diagnosis was changed from renal to absorptive hypercalciuria. Both of these patients had creatinine clearance rates less than 60 percent of normal during the first test. One also had multiple residual stones during both evaluations, and the second had a urinary tract infection during the first test that resolved with a normal creatinine clearance by the second test period. When nephrogenous cyclic adenosine monophosphate (cAMPn) assays were done on fasting specimens in these patients, the results were consistent with absorptive hypercalciuria. Almost all patients can be evaluated and placed in management programs within a few weeks after surgery. If cAMPn assays are not done, patients with decreased renal function secondary to residual stones or infection can be tested at a later time. 