Pityrosporum orbiculare, Candida albicans, Staphylococcus epidermidis and S. aureus were irradiated with UVA and UVB light in vitro. UVB inhibited growth much more effectively than UVA. P. orbiculare was the most sensitive and S. aureus the least sensitive organism. With a dose of 900 mJ cm-2 of UVB a 50 times reduction in number of colony forming units was seen for S. aureus and for the other organisms a total inhibition of growth was seen. When P. orbiculare was irradiated with monochromatic light at 300, 330 and 360 nm the highest antimicrobial activity was seen at 300 nm. If these in vitro observations correlates with the effect of UV-light treatment of various skin disorders is still unclear.