Rat epididymal sperms were collected after 7 weeks of treatment with Tripterygium wilfordii monomers T4,T7,T15 and triptolide. Total nuclear basic protein (TNBP) were extracted from sperm nuclei isolated by sonication. The relative proportions of histones and protamine were determined by scanning microdensitometry following electrophoresis of TNBP in polyacrylamide gels. It was found that the content of TNBP was reduced while the total histone/protamine ratios were increased following treatment, indicating a marked decrease of protamine levels as compared with the control group. These results suggest that the interruption of nuclear protein transition of spermatids induced by T4,T7,T15 and triptolide might lead to infertility.