Five partially hydrogenated derivatives of dibenz[a,h]anthracene (DBA) were tested (or inhibitory action on skin tumorigenesis by DBA, by simultaneous application to the skin of Swiss female mice. Solutions containing 0.06 percent of DBA together with 0.2 percent of the hydrogenated derivative in acetone-benzene (9:1) were applied twice weekly for 50 weeks. Of the compounds tested, 5,6-dihydro-DBA, 1,2,3,4,8,9,10,11-octahydro-DBA, and 1,2,3,4,1a,4a,5,6,8,9,10,11-dodecahydro-DBA showed a moderate inhibitory action; 5,6,12,13-tetrahydro-DBA had no inhibitory activity and 1,2,3,4,12,13-hexahydro-DBA, which is carcinogenic when tested alone, appeared to have an enhancing effect on DBA carcinogenesis.