A simple method for antigen retrieval in tissue sections and cell cultures is described. Because many antibodies recognize denatured proteins on western blots, but are poorly reactive by immunocytochemistry, the effect of applying sodium dodecyl sulfate (SDS) to cryostat sections of tissues and to cell cultures prior to immunostaining was examined. In many cases, a 5-min pretreatment with 1% SDS produced a dramatic increase in staining intensity by indirect immunofluorescence. Among the antibodies tested that showed a positive effect of SDS were an anti-Na/K-ATPase monoclonal antibody, an anti-AE1/2 anion exchanger polyclonal antipeptide antibody, a monoclonal anti-caveolin antibody, and an anti-rab4 monoclonal antibody. In other cases, including antibodies against gp330, aquaporin 1, and aquaporin 2, no effect of SDS was detected. The results show that SDS treatment can be used as a simple method of antigen retrieval in cryostat sections and on cultured cells. In some cases, antigens were not detectable without pretreatment with SDS.