Proteolysis, a regulated biological process, is reflected by protein spot molecular weight distribution in 2-D gel electrophoretograms. Here we report studies of Streptomyces cultures as they undergo two different developmental processes involving proteolysis. Systematic changes in protein molecular weight distribution between the control samples and those with high activity of proteases were demonstrated. The observations were supported by a numerical model of degradation and its influence on the M(r) distribution. Simple statistics could be used to distinguish between normal and degradative 2-D gel electrophoretic patterns.