The fungus produced 5 spore stages on red raspberry and overwintered as teliospores adhering to canes. In the field spermagonia appeared in a single flush in early summer on leaves of the primocanes (first-year canes) and on leaves of the lateral shoots of fruiting canes, and were followed by aecia, uredia and telia. Aecia and uredia occasionally appeared on petioles and sepals and uredia on drupelets of mature fruits. Lesions caused by aecia and uredia on the bases of primocanes did not become cankerous in the following fruiting year. Necroses associated with large aecia produced a shot-hole effect and leaflets heavily affected by either aecia, uredia or telia abscissed prematurely. The sequence of spore stages on pot-grown plants inoculated with mature overwintered teliospores took 60 d to the reappearance of telia. The rate of development of uredia and associated necroses was faster on younger than on older leaves but the cumulative spore yield was not significantly different. Opt. temp. for germination of urediospores in vitro (18.4-20.9C) was higher than for mature teliospores (14.6-18.4C). Light inhibited germination of both types of spores. Teliospore germination was inhibited by wavelengths of 590-750 nm, but this was partially reversible under other light conditions. A reversible inhibition of basidiospore formation was also observed under shorter wavelengths.