We compared results for total bilirubin as measured on a coated thin film and by the Evelyn-Malloy and Jendrassik-Gróf methods. We examined serum samples from patients and studied the effects of protein, hemoglobin, and lipids on bilirubin measurement. Results from the thin-film assay compared favorably with those of the other methods. Total and within-day precision (CV), assessed over a one-year period, were better than 6% and 3%, respectively, at all concentrations. Analytical recovery was 99 +/- 3%. Samples from individuals having a wide range of liver diseases demonstrated, by linear regression, good correlation between the thin-film method and the two wet-chemistry methods (correlation coefficients of 0.990 and 0.994). We conclude that the thin-film method offers a valid alternative assay for total bilirubin.