In spite of several biomedical applications of polyurethanes, very little attention has been focused on these polymers for controlled drug delivery. In this study, an aliphatic polyurethane, Tecoflex(R), was evaluated as a microsphere matrix for the controlled release of theophylline. Polyurethane microspheres containing theophylline were prepared using a solvent evaporation technique from a dichloromethane solution of the polymer containing the drug. A dilute solution of poly(vinyl alcohol) served as the dispersion medium. Microspheres of good spherical geometry having theophylline content of 35% could be prepared by the technique. The release of the drug from the microspheres was examined in simulated gastric and intestinal fluids at 37 degrees C. While a large burst effect was observed in gastric fluid, in the intestinal fluid a close to zero-order release was seen. Attempts were made to modulate the release by incorporating poly(ethylene glycol) in the matrix and also coating the spheres with paraffin wax. Preliminary data indicate that polyurethanes could be interesting matrices for controlled drug delivery.