To the Editor: We should like to comment on the recent paper of Johnson et al. (N Engl J Med 295:1214, 1976). The authors present evidence that in acute pancreatitis a renal mechanism (some “tubular-dysfunction factor”) is responsible for the enhancement of the amylase-to-creatinine clearance ratio (Cam/Ccr ratio) rather than an isoamylase abnormality. They state that there is no available information whether this “factor” functions in conditions other than acute pancreatitis. Earlier reports from several authors and recent findings of our groups have case doubt on the diagnostic value of the Cam/Cer ratio.