This study investigates in vitro the drug delivery characteristics of new thermo-sensitive gels, P-CS/GA gels, in which a chitosan (CS) network is crosslinked with various concentrations of glutaraldehyde (GA) that interpenetrates Poloxamer (P) gels. The results indicate that the swelling ratios of all P-CS/GA gels are markedly superior to those of non-swelling P and P-CS gels. For example, P-CS/GA (0.1 wt.%) gels have swelling ratios of 13.2+/-1.0, which are maintained for approximately 18 h in water at 37 degrees C. In vitro releases of 5-FU from P-CS/GA (0.1 wt.%) gels had significantly lower initial burst release (P<0.01) and lasted much longer than those from gels without a CS network. For example, the duration of release of 5-FU was in a significantly sustained manner for up to 52 h, which was about 10 times or longer than the period of delivery using P or P-CS gels. The release of drugs from gels with an interpenetrating CS network could be modeled by Fickian diffusion; the characteristic constant 'k' of drug-gel systems decreased as increasing GA concentrations in the P-CS/GA gels, and increasing the viscosities of the P, P-CS and P-CS/GA solutions.