Serial measurements of total creatine kinase (CK) and the MB isoenzyme of CK (CK-MB) were performed on 18 stable hemodialysis patients over a 36 month interval in a longitudinal study designed to examine CK and CK-MB variability. Total CK was measured by the DuPont ACA pack procedure. CK-MB was quantitated by the ACA CK-MB ion exchange pack procedure, and by electrophoresis. The mean CK level was 242 +/- 179 IU/l (+/- SD). The mean CK-MB level was approximately 8% of the total CK. Seventy-two percent of the patients had at least one elevated CK level during the course of this study. Depending upon the method of analysis, 88 to 100% of the patients had at least one elevated CK-MB level. Marked and sporadic variations in both total CK and CK-MB levels were apparent, but were not related to the assay. Patients receiving long-term intramuscular androgens had higher CK, but not CK-MB, than did hemodialysis patients not receiving these agents. Discontinuation of the intramuscular androgens for four weeks led to a fall in CK in only one of four patients. Therefore there appears to be a biological effect of exogenous androgens which may play a role in elevating CK in hemodialysis patients.