Dictamnine, a furoquinoline alkaloid of the Rutaceae plant family, has been shown to be mutagenic and phototoxic in bacteria and yeasts. Here, we have investigated the phototoxic effect of dictamnine in human Jurkat T cells and HaCaT keratinocytes. Dictamnine was isolated from the roots of DICTAMNUS ALBA L. and was photoactivated with solar simulated radiation, delivered from a 1000-W xenon arc lamp with a maximal output between 300 - 800 nm. Dictamnine displayed concentration- and light-dependent phototoxic effects in both cell lines. In comparison to the structurally related furocoumarins 5-methoxypsoralen and 8-methoxypsoralen, dictamnine was less phototoxic. Nevertheless, it may play a major role in the elicitation of phytophotodermatitis because of its abundance in plants of the Rutaceae family.