Porous biodegradable polymeric foams loaded with drugs have potential applications in tissue engineering and sustained delivery systems. A single-step process using supercritical CO2 as a foaming and carrier agent was used for the impregnation of 5-fluorouracil in polylactide and poly(lactide-co-glycolide) probes. The release of 5-fluorouracil from the probes for 24 h at 37 degrees C and pH 7.4 was followed by measurement of the amount of drug released to the media and a change of the probes weight. In order to gain further insight into the drug-release mechanisms, a mathematical model (not previously described in the literature) is proposed to quantitatively describe the process of drug release. Our model considers that the release process goes through three different steps controlled first by external diffusion, second by internal mass transfer, and third by polymer degradation. The theoretical curves agreed fairly well with the experimental drug-release profiles.