Some modifications of the conditions of the reaction between plasma and bromcresol green have led to an improved method for determination of plasma albumin with the Vickers M300 multichannel analyzer. Dye concentration and reaction time are the factors principally influencing method specificity, but variable protein composition of human plasma also affects it, so that optimal reaction conditions vary from specimen to specimen. Thus a compromise must be reached such that the best conditions for determining plasma albumin over a range of different protein concentrations are achieved. In the proposed method for the Vickers M300 a reaction time of 12 s (the minimum possible) is used. Comparison with "rocket" immunoelectrophoresis gave the following linear regression: y = 10 + 0.79 x (n = 91; r = 0.96).