Three methods were used to determine the enhancement by sodium dodecyl sulfate (SDS) of prodigiosin formation in Serratia marcescens O8. The results of the agar disk diffusion method indicated that pigment formation was dependent upon the concentration of SDS. Diameters of the pigment zones were proportional to the logarithm of SDS concentrations of 300 to 1,500 mug/ml. When bacteria were grown in broth containing SDS from 0 to 800 mug/ml and the pigment extracts were analyzed spectrophotometrically, a similar enhancement of pigment formation was observed. Finally, these results were confirmed by high-performance liquid chromatographic analysis of the extracts. Prodigiosin appeared to be the sole component with increased synthesis. The possible mechanism of the SDS enhancement effect could be explained by an increase in negative binding sites by the association of SDS with a cell envelope component(s). These binding sites may be required for prodigiosin synthesis.