To determine whether alteration of PKCα expression would affect the metastatic potential of human melanoma cells, replicate cultures of C8161 cells were treated in vitro with a phosphorothioate antisense oligodeoxynucleotide (ODN) that specifically inhibits PKCα expression (ISIS-3521). Control C8161 cultures were treated with a scrambled sequence ODN, cationic liposomes or were left untreated. Northern blots demonstrated 70% inhibition of PKCα mRNA in ISIS-3521-treated cells compared to controls. Metastasis was suppressed by 75% when ISIS-3521-treated cells were injected intravenously into athymic mice. These results show that PKCα expression is important in the regulation of human melanoma metastasis.