Tributyl phosphate was tested for skin sensitization in Hartley guinea pigs (10/sex) exposed dermally to 0.30 ml of a 10% (w/v) mixture in mineral oil for 6 hours, once weekly for 3 weeks. An additional 10 animals (vehicle control group) received a similar treatment with mineral oil only. Fourteen days after the third induction treatment, the treated animals were challenged with the test material at a virgin site; an additional 10 animals, not previously exposed, received a similar challenge exposure with the test compound. The vehicle control group was challenged with mineral oil. Animals were examined for erythema at 24 and 48 hours after the challenge exposure. The treatment, challenge control, and vehicle control groups did not display sensitizing reactions (erythema/ eschar and edema scores of 0). Tributyl phosphate was non-sensitizing after dermal application in guinea pigs.