We investigated the influence of assay protocol upon results of Coomassie Brilliant Blue protein dye-binding assays for urinary protein. Sensitivity and working range for, and linearity of response (including dilution dependence) of, three standard assays and four micro assays to bovine albumin, gamma-globulin, and urine are compared. The Read and Northcote standard assay (Anal Biochem 1981; 116:53-64) appears to be the method of choice.