Secondary embryogenic potential of winter oilseed rape, Brassica napus ssp. oleifera (Metzg.) Sinsk. cv. Primor, was maintained for over six years without diminution. Cytological analysis of 22 randomly selected secondary embryoids showed that they were all haploid. Many factors affect secondary embryogenesis in culture. The frequency of secondary embryogenesis was enhanced by the incorporation of 15 g l−1 sucrose into the medium; sucrose at 60 to 120 g l−1 inhibited secondary embryogenesis. Incubation in continuous darkness or continuous light led to a marked suppression of secondary embryogenesis. The best light regime for secondary embryogenesis was 16 h light/8 h dark. Incorporation of activated charcoal into the culture medium and the application of gamma radiation suppressed secondary embryogenesis. Further secondary embryogenesis was significantly reduced when only part of the secondary embryoid was cultured. The results discussed are based on the possibility that endogenous growth regulators may be involved in the initiation of secondary embryoids.