The effect of 13-cis-retinoic acid (13-cis-RA) on 1,2-dimethylhydrazine (DMH)-induced colon cancer in male, random bred, Sprague-Dawley (S-D) and inbred Wister/Furth (W/Fu) rats and on isograft tumor growth and metastases in a Brown Norwegian (BN) X W/Fu F1 rat was studied. 13-cis-RA (300 mg/kg diet) was administered to S-D rats 1 week before commencing DMH injections and for the duration of the experiment. W/Fu rats received 13-cis-RA (10 mg/kg weight X 5 days) 6 weeks after DMH injection had begun and monthly thereafter. Primary tumors were detected by serial laparotomy under ether anesthesia in both strains. The time to tumor onset was significantly delayed in treated groups, S-D and W/Fu, P = 0.0339 and 0.0322, respectively (Mantel-Haenszel test), compared with placebo-treated controls. 13-cis-RA (15 mg/kg weight) administered 2 days before and for the duration of isograft tumor growth (DMH 2054, a well-differentiated mucin-producing colon adenocarcinoma that spontaneously metastasized to lung) had no effect on tumor growth or metastasis in the BN X W/Fu F1 rat. The findings suggest that the role of 13-cis-RA is in colon cancer prevention and not in its treatment either in an adjuvant or established setting.