This paper describes a trial of the Canterbury GP After-Hours Service (CGPAHS), a GP staffed after-hours service within the Canterbury Hospital Emergency Department. It was decided not to continue the service beyond the twelve-month trial phase because the opportunity cost to do this was greater than existing alternative services. The efficiency of the service might have been improved had greater numbers of patients been referred to it, either from the adjacent emergency department or the local community. Reasons why the trial was not able to realise these efficiencies are explored.