A process is described by which hydrocephalus shunt catheters can be impregnated with antimicrobials. The processed catheters showed antimicrobial activity at their surfaces for long periods and could be sterilised by autoclaving. When tested in vitro in a model of catheter colonisation using large challenge doses of Staphylococcus epidermidis and prolonged perfusion, some antimicrobials failed to protect against colonisation whereas others protected against one or two challenges. A combination of rifampicin and clindamycin gave best results, protecting against three successive challenges over a 28 day perfusion period. Resistant organisms did not develop. The process is likely to be useful in prevention of hydrocephalus shunt infection.