The benefits of supplementary ultraviolet radiation (UVB: 280-320nm) in protected lettuce were investigated in controlled environment studies. Exposure to UV-B prior to inoculation with a conidial suspension of Bremia lactucae (lettuce downy mildew) led to significant reduction in the subsequent sporulation of the pathogen. In addition to disease control, UV treatments increased leaf thickness, reduced leaf area and increased leaf pigmentation in a red-leaved cultivar. Such changes in leaf area and thickness are important quality factors that would be expected to improve plant performance after transplantation into the field. The aim of further studies will be to test such findings in a commercial glasshouse environment.