The effects of different culture conditions (medium, growth regulators and irradiance) on the development of Chondrus crispus sporelings were investigated. All three factors had significant effects on the percentage of spores which germinated and/or on the growth of erect axes. Statistically significant interactive effects (medium x irradiance, medium x time and medium x growth regulator) were also found. Maximum spore germination and growth of young shoots were obtained in Swm-t medium containing 1 mg L^-1 of benzylaminopurine under an irradiance of 20 µmol photons m^-2 s^-1. The highest irradiance tested, 30 µmol photons m^-2 s^-1, caused discoloration of disc-stage sporelings and greatly reduced their viability, but on the other hand, under this irradiance, growth of erect axes of more than 5 mm in length was highest in Swm-t medium containing 1 mg L^-1 of indole-3-acetic acid and naphthalene-acetic acid.