I describe a rapid, sensitive immunoturbidimetric assay for measuring urinary albumin and immunoglobulin G with use of an automated spectrophotometer. Diluted urine samples and polyethylene glycol in phosphate-buffered saline are pipetted into the cuvettes of the spectrophotometer. The initial absorbances of the samples are measured at 340 nm; antiserum to albumin or to immunoglobulin G is added to each tube, and after 2 min at 37 degrees C the absorbance of the mixtures is read at 340 nm. The initial blank absorbances of the samples are subtracted from the final absorbances automatically. The change in absorbance is linear with concentration in the range of 5-400 mg/L for albumin and 3-1000 mg/L for IgG. The lower limit of the determination is 5 mg/L for albumin, 3 mg/L for IgG. Linear correlations were observed between the concentrations of albumin and immunoglobulin G determined by this method (x) and those determined by radial immunodiffusion (y). The regression equation for albumin was y = 0.84x + 0.03 (r = 0.99, n = 87), and for IgG y = 0.94x + 0.02 (r = 0.98, n = 87).