The pathway of anthocyanin biosynthesis is well known while its regulation is less characterized. In this paper we focus our attention on the process of anthocyanin photoinduction. The results obtained following irradiation of seedling root tissues with lights of different quality disclose a significant response to blue light, apparently not attributable to phytochrome action. Even when anthocyanin accumulation is significantly increased because of the presence of Pl, a pigment intensifier, the total phytochrome content is not affected. The blue light effect is general in the sense that is observed in all genetic backgrounds tested. Photoinduction of anthocyanin accumulation in viviparous mutants blocked in carotenogenesis depends on blue light indicating that carotenoids are not involved in the blue response. Studies with calcium-channel blockers and calcium antagonists seem to exclude a requirement of Ca++ as an intermediary component of the light transduction pathway.