We previously showed that fenretinide (4-HPR), a synthetic derivative of all-traits retinoic acid (RA), is effective in mice bearing the human ovarian carcinoma IGROV-1 and it significantly enhances the antitumour activity of cisplatin on the same tumour. The present study examined the therapeutic effects of the combination of 4-HPR and RA and of the two retinoids with cisplatin as intracavitary treatments of mice bearing IGROV-1 and IGROV-1/cisplatin tumours, the latter derived from a sub-line with an in vivo reduced sensitivity to cisplatin. 4-HPR, as a single agent, was effective against both tumours, whereas RA had no effect. In IGROV-1 tumour-bearing mice, the combination of RA and 4-HPR significantly improved the efficacy of 4-HPR, resulting in an antitumour activity similar to that obtained with cisplatin alone. N-(4-methoxyphenylretinamide), the main metabolite of 4-HPR, had no antitumour effect and it did not increase 4-HPR activity in IGROV-1 tumour-bearing mice. In the same tumour model, 4-HPR and RA separately increased cisplatin activity, even though for RA the increase was not statistically significant. In contrast, the association of the two retinoids together with cisplatin did not produce any benefit and resulted in increased toxicity. In IGROV-1/cisplatin tumour-bearing mice, the association of 4-HPR (but not of RA) to cisplatin significantly increased cisplatin activity, resulting in the reversal of cisplatin resistance. These findings demonstrate that 4-HPR may be effective and enhance cisplatin sensitivity in cisplatin-sensitive and -resistant ovarian tumours and that the association of RA and 4-HPR may result in increased 4-HPR antitumour activity.