Sodium polyanethol sulfonate (SPS) is an anionic detergent with a broad range of activities and applications. While studying the excretion of cytoplasmic proteins in Staphylococcus aureus SPS was used as cell lysis inhibitor. When investigating the protein pattern of culture supernatants from cells grown in the absence or presence of SPS by Coomassie blue stained polyacrylamide gel the amount of protein bands was significantly decreased in the presence of SPS, suggesting that this effect was due to inhibition of cell lysis. However, various control studies showed that the apparent decreased protein secretion was an artifact due to the interference of SPS with Coomassie blue- and silver-staining. The only alternative method that was uninfluenced by SPS was imidazole-SDS-zinc staining. This is the method of choice particularly when protein interfering compounds are present in the extracts. For protein quantification in liquid samples the bicinchoninic acid (BCA) assay appeared to be the method of choice in the presence of SPS. The assay is based on neutral peptide bonds and is therefore rather insensitive to interfering compounds. This study shows that SPS and most likely also related detergents might falsify conventional protein staining and quantification methods.