The bincinchoninic acid protein assay has been adapted for use with microtiter plates and a plate reader to reduce the time needed for analyses. The total volume of the assay was reduced to 0.21 ml with various ratios of sample to reagent volume being used. The assay is sensitive to a limit of less than 1 microgram of bovine serum albumin. The assay is insensitive to the presence of the detergents sodium dodecyl sulfate, Triton X-100, and deoxycholate. In addition, the method has been adapted for determining the protein concentrations of sucrose density gradient fractions, which eliminates the need for removing the sucrose prior to assay.