Because folate receptor alpha (FRalpha) is frequently over-expressed in epithelial ovarian tumors, we hypothesized that its association with folate may differ by FRalpha expression or by the timing of intake. We examined the association between folate and other cofactors in 152 ovarian cancers evaluated for FRalpha expression from the Nurses' Health Study. Multivariate odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using unconditional logistic regression. FRalpha expression was higher in serous invasive and advanced stage ovarian tumors. Recent dietary folate intake > or = 300 microg/day compared to < 300 microg/day was associated with decreased risk of developing ovarian cancer (OR = 0.62; 95%CI 0.40-0.96). There was suggestion of an increased risk with total folate (dietary and supplemental) (OR=1.42; 95%CI 0.94-2.14 for past and OR = 1.53; 95%CI 0.99-2.37 for recent intake). These results did not vary by FRalpha status of the tumor. Methyl group score, a marker of high dietary folate and methionine intake but low alcohol consumption, was inversely associated with risk of ovarian cancer (OR = 0.44; 95%CI 0.23-0.84 for past and OR=0.46; 95%CI 0.24-0.88 for recent intake). There were no clear individual associations between methionine, vitamin B(6), or multivitamin use and ovarian cancer risk overall or by FRalpha tumor status. Our data do not support the hypothesis that the relationship between factors involved in one-carbon metabolism and ovarian cancer risk differs by FRalpha status of the tumor.