Two experiments assessed the effect of current and elevated levels of ultravioletB (UV-B) radiation on forage crop production. The effect of current levels of UV-B radiation was assessed by comparing the growth of eight cultivars of four legume and four grass species for three growing seasons (1994–96) under simulated sward conditions in the field. An exclusion system using cellulose diacetate or polyester covers provided comparable growing conditions for the plants, except for the presence or absence of ambient UV-B radiation, respectively. The second experiment studied the effect of elevated levels of UV-B on eight cultivars of two legume and two grass species in the greenhouse under simulated sward conditions. Natural lighting with sufficient supplemental light was used to provide ideal growing conditions for a 16-h day length. Separate sets of UV lights were installed to provide UV-B levels at approximately the same intensity as would be found in mid summer, and 33% and 66% more than this value. A fourth treatment consisted of removing UV-B radiation by using a polyester filter. Plant production was measured in both experiments. In 1994, field herbage yields from all young grass and legume seedlings were not significantly affected by the exclusion of ambient UV-B radiation, with the exception of alfalfa. Intra-specific variations with alfalfa yields were found for reduced levels of UV-B radiation. In general, these trends persisted as stands matured during two post seeding years. In the second experiment, no significant differences were observed for all tested species with increasing levels of UV-B radiation, except with some alfalfa cultivars and one birdsfoot trefoil cultivar. Collectively, these results demonstrate that in the northern latitudes young and mature plants of the studied species are resistant to current and potentially higher levels of solar UV-B radiation, with the exception of some alfalfa cultivars. The yield of these cultivars increased under enhanced levels of UV-B radiation in the greenhouse and decreased when UV-B was excluded in the field.