The efficacy of a 5% solution of para-aminobenzoic acid (PABA) to protect against photocarcinogenesis was tested in 6 groups, each of which contained 30 light pigmented hairless mice. The light source was a Phillips TL 40 W/12, which mainly emits UVB. PABA significantly retarded the tumor induction time (p less than 0.05) and reduced both tumor yield and carcinoma yield (p less than 0.05). The dorsal skin of the mice was removed and weighed. The mean weight of UVR-exposed mice skin protected with PABA did not differ from that of the controls, but in the non-protected UVR-exposed mice the skin samples were significantly heavier (p less than 0.05).