D&C Red No. 36, a drug and cosmetic dye commonly used for coloring lipsticks, was evaluated for its carcinogenicpotential in male and female Wistar rats. This dye has been shown to exhibit mutagenic activity towards Salmonellatyphimurium TA 98 in the presence of S9 mix. In the present study, 50 male and 50 female rats in each group weregiven diets containing D&C Red No. 36 at 2 different concentrations, 1,000 ppm and 2,000 ppm, for 78 weeks andsacrificed at week 98.It was found that dye treatment had no significant effect on the survival of either male or female animals as wellas the body weight gain in males. However, body weight gain of treated females was slightly lower than that of thecontrol group. Histopathological assessment demonstrated a number of benign and malignant tumors to havedeveloped in various organs of both dye treated and control groups. In male rats, benign liver tumors were found atincidences of 16.7% and 18.8% of the low (1,000 ppm) and high (2,000 ppm) dose groups, respectively, similar to the20% for the control group. Malignant tumors of the thyroid gland were observed only in the low dose and controlgroups, at 4.2% and 2%, respectively. In the high dose group, the incidences of lung, liver, urinary bladder and softtissue cancers were 4.2%, 2.1%, 2.1% and 2.1%, respectively, only one soft tissue cancer being observed in a controlgroup animal. In females, benign tumors were observed in the liver and mammary glands. The incidences of livertumors in the low and high dose groups were 12.8% and 16%, respectively, and 6% in the control group. Values formammary gland tumors were 10.6%, 10%, and 18% respectively. Malignant tumors were also observed in variousother organs, including the uterus, lung, kidney, thyroid, thymus and salivary gland, but the incidences were verylow (about 2-4%) and in dye treated male and female rats were not statistically different from those in the controlanimals.The results of the present study thus demonstrated that D&C Red No. 36 at the concentrations of 1,000 ppm and2,000 ppm in the diet is not carcinogenic either to male or female Wistar rats. While the occurrence of benign livertumors in female rats may be related to dye treatment, the lack of any apparent dose-dependence or any statisticallysignificant difference from the control group (P = 0.06) suggests that this is unlikely.