A case-control study of dietary factors and cancer of the ovary was conducted during 1989-92 in metropolitan Toronto and surrounding areas of southern Ontario, Canada. Four hundred and fifty women aged 35-79 years, with newly diagnosed, histologically verified, primary epithelial ovarian-cancer were interviewed concerning reproduction and diet. Over the same period, 564 randomly-selected population controls, frequency-matched to the cases within three 15-year age groups, also were interviewed. From information obtained by quantitative diet history, average daily macro- and micronutrient intake values were calculated through use of the United States Department of Agriculture Food Composition Databank, which was extended and modified for Canadian items and recipes. Analysis was performed with continuous, unconditional logistic-regression methods, adjusting for age at interview, number of full-term pregnancies, total duration of oral contraceptive use, and total daily caloric intake. Neither reported history of lactose intolerance, nor average daily consumption of lactose or free galactose, were found to be associated with risk of ovarian cancer. Lactose intake or intolerance did not appear to modify the protective effects of parity and oral contraceptive use. Nevertheless, other studies suggest that ovarian galactose metabolism still may have a relationship with risk of ovarian cancer, though more evidence is needed.