We have analyzed and compared the cyclosporine concentrations in whole blood specimens from heart and kidney transplant patients, using three different methods: high-performance liquid chromatography (HPLC), polyclonal radioimmunoassay, and monoclonal radioimmunossay. HPLC results for heart transplant patients correlated well with the monoclonal (specific antibody) results but did not correlate with the polyclonal (nonspecific antibody) results. All three methods correlated well for renal transplant patients; however, polyclonal results were consistently higher than either monoclonal or HPLC results. We conclude that the results from the monoclonal (specific antibody) RIA are equivalent to HPLC results for both kidney and heart transplant patients.