We describe microplate methods for measurement of human urinary albumin (HUA) by competitive enzyme-linked immunosorbant assay (ELISA) and creatinine with a modified commercial enzymatic kit. Incorporation of substrate mixing into the competitive ELISA changes the dynamic absorbance-concentration response, greatly simplifying calculations and improving sensitivity and accuracy. Measurement of creatinine in urine and plasma samples with a commercially available enzymatic kit modified for analysis by use of an inexpensive microplate reader produced values comparable in precision and accuracy to those obtained by an automated kinetic Jaffé method.