Antibiotics will reduce infection in medica I textiles. The uptake of quinoline antibiotic under batch dyeing conditions by a polyurethane containing carboxylic acid groups was compared to that of unmodified material, and optimized by variation of pH, electrolyte, time, temperature, and liquor ratio. The mechanism of interaction is suggested by the dyeing isotherm. Zones of inhibition showed antibiotic release by the "dyed" material beyond 96 hours versus 10 minutes for the unmodified material. A low value for the affinity of the antibiotic for the polyurethane was calculated. On a fiber, this value represents poor fastness, but for medical materials,this provides the desired sustained antimicrobial properties. A potential exists for optimizing release in vitro rather than by using in vivo testing.