We evaluated the performance characteristics of the Beckman Creatinine Analyzer 2, a kinetic colorimetric analyzer which utilizes a modified Jaffé reagent. The instrument gave linear measurements to at least 300 mg/L and its within-run precision on a 50 mg/l creatinine standard was 1.1%. Its between-day precision on the 50 mg/L creatinine standard was less than 5.0%. Its results correlated well with those from the manual Jaffé. CentrifiChem System 400, TechniconTM SMATM 6/60 System, and TraceTM systems I and III. Interferences from 19 possible serum constituents and 32 drugs were almost nonexistent. The extended linear range of the Creatinine Analyzer 2 allowed the direct assay of samples from patients undergoing periodic hemodialysis.