This study was designed to evaluate the pharmacologic and biological properties of a paclitaxel-hyaluronan bioconjugate (ONCOFID-P) against IGROV-1 and OVCAR-3 human ovarian cancer xenografts following i.p. administration. In vitro tumor sensitivity to ONCOFID-P was analyzed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, whereas bioconjugate interaction with cells was studied cytofluorimetrically and by confocal microscopy. In vivo toxicity was assessed by a single-dose maximum-tolerated dose, peripheral blood cell count determination and by histologic analysis. Biodistribution of the compound was evaluated with a small animal-dedicated scintigraphy gamma camera following injection of 99mTc-labeled ONCOFID-P. Pharmacokinetic analysis was also carried out. Female severe combined immunodeficiency mice implanted with ovarian cancer cells underwent treatment with ONCOFID-P or free paclitaxel starting from day 7 or 14 after tumor injection, and survivals were compared. ONCOFID-P interacted with CD44, entered cells through a receptor-mediated mechanism, and exerted a concentration-dependent inhibitory effect against tumor cell growth. After i.p. administration, the bioconjugate distributed quite uniformly within the peritoneal cavity, was well-tolerated, and was not associated with local histologic toxicity. Pharmacokinetic studies revealed that blood levels of bioconjugate-derived paclitaxel were much higher and persisted longer than those obtained with the unconjugated free drug. Intraperitoneal treatment of tumor-bearing mice with the bioconjugate revealed that ONCOFID-P exerted a relevant increase in therapeutic activity compared with free drug. ONCOFID-P significantly improved results obtained with conventional paclitaxel, in terms of in vivo tolerability and therapeutic efficacy; these data strongly support its development for locoregional treatment of ovarian cancer.