The role of retinoic acid receptor (RAR) expression in sensitivity to N-(4-hydroxyphenyl)retinamide (4HPR or fenretinide) as well as on the tumorigenicity of human ovarian carcinoma cells was examined. Two human ovarian cancer cell lines, A2780 and IGROV-1, with a 10-fold difference in sensitivity to 4HPR were chosen to study RAR involvement in the response to 4HPR. To determine which RAR was effective, RAR␣,  and ␥ were individually overexpressed in A2780 cells, which are the most sensitive to 4HPR. Sensitivity to 4HPR was increased in RAR-overexpressing clones, whereas it was slightly decreased in RAR␣ transfectants (which had diminished RAR expression) and was unchanged in clones transfected with RAR␥. IGROV-1 cells, which are RAR negative, were transfected with RAR. Surprisingly, none of the obtained IGROV-1 RAR transfectants expressed RAR protein, in spite of RAR mRNA transcription. All clones were similar to the parental IGROV-1 cells in their sensitivity to 4HPR. Treatment with a pharmacologically achievable concentration of 4HPR (1 M) led to a rapid 2-fold increase in RAR mRNA levels in A2780 cells, but it did not induce RAR expression in IGROV-1 cells. Analysis of the tumorigenicity of A2780-transfected clones revealed that overexpression of RAR␣ was associated with a significant reduction in tumor takes (50% and 67%, respectively, vs. 96% for the parent line) and with a reduced growth rate. Oncogenicity was clearly decreased in only 1 of the 2 RAR-overexpressing clones (33% takes) and was unchanged in the 2 clones with increased RAR␥ expression. Our results demonstrate that basal expression and 4HPR inducibility of RAR play a role in mediating 4HPR response in ovarian cancer cells. The findings of reduced oncogenicity of clones overexpressing RAR␣ and of one clone overexpressing RAR indicate that RAR␣ and RAR might have a tumor-suppressive effect in ovarian tumors.