Metalloproteases are implicated in conferring invasive properties to tumor cells. We show here that treatment of ras-oncogene-transformed rat fibroblasts with dimethylsulfoxide (DMSO) results in a reversible decrease in stromelysin mRNA. Furthermore, stromelysin expression was found to be repressed by DMSO, but not by glucocorticoid hormone, in a fibrosarcoma cell line showing low AP-1 (fos/jun) transcription factor activity. In two fibrosarcoma cell lines which express high levels of stromelysin and low levels of 68 kDa type IV collagenase, the DMSO-induced decrease in stromelysin expression was paralleled by a decreased invasive propensity.