We have studied the effect of several factors that influence recombinant protein production, by using the expression of recombinant streptolysin-O as our model. This protein, produced by Streptococcus pyo genes, is important in the biotechnological industry, where it is used to pro duce immunodiagnostic reagents. In order to improve the yield of this pro tein, we tried an alternative production method using strains of Escherichia coli and recombinant DNA technology. We have evaluated this method at the laboratory scale, taking into account factors such as inductor concen tration, temperature of induction, proportion of culture medium volume to total flask volume, and strain of Escherichia coli used. To this end we applied techniques of experimental design, particularly a "fixed-effects bi factorial design”, with the expression level of recombinant streptolysin-O in E. coli being the response to the factors. All the effects studied were found to be significant and relevant to the economics of the protein production.