A novel melanogenic inhibitory compound, Phytoclear-EL1 (5,10-diacetyl-3-benzoyllathyrol) was isolated from Euphorbiae lathyridis. The effects of EL1 on culture normal human melanocytes (NHM) were assessed. EL1 reduced the melanin synthesis of NHM by 40% at a concentration of 2 $square$g/ml without any apparent cytotoxicity. We also have found that the treatment of the cells with EL1 decreased the tyrosinase activity by 29% in situ. To elucidate the action mechanism of EL1, we investigated the changes in mRNA levels of tyrosinase, TRP-1 and TRP-2 using RT-PCR technique. AS a result, the mRNA levels of tyrosinase, TRP-1 and TRP-2 were markedly reduced by EL1 treatment. These results suggest that Phytoclear-EL1 is a novel whitening agent that is effective in human melanocytes.