Measurements of ammonia gas concentration at Cape Grim (40¿41'S, 144¿41'E) have been made during six field expeditions between February 1978 and May 1980. For this coastal site a clear distinction between maritime and continental winds were evident in the observed ammonia concentrations. While continental winds gave concentration comparable with those generally reported in the northern hemisphere (~1 μg m-3, STP), maritime winds gave much lower concentrations (mean 0.06 μg m-3, STP). No large seasonal trend was apparent in the latter data.