Ultra-violet (UV) treatment has been shown to inactivate hepatitis A virus (HAV) in wastewater and polluted drinking water. Whether this method could be used to inactivate virus preparations made for vaccine purposes is not known since the effect of UV on the antigenicity of HAV has not been studied. HAV vaccine preparations have been treated effectively with formaldehyde. However, this method is time-consuming, since treatment times of up to 15 days have been published as necessary for a complete and safe inactivation. We used a cell-culture-derived HAV preparation with a TCID50 of 10(9) for a UV irradiation experiment. The antigenicity (assessed by a panel of anti-HAV antibodies), viral genome titre (quantitated by polymerase chain reaction) and HAV infectivity were compared after treatment with UV doses of 0, 184, 368, 552, 736 and 920 J m-2. Our results showed the antigenicity of HAV was almost unaltered even when infectious viral particles were no longer detectable. This technique shows potential as a simple and low-cost method for an inactivated HAV vaccine.