The study was performed to get the basic knowledge about the changes of the cyclic AMP concentration and protein contents in cultured human melanocyte during 7 weeks of cultivation. The results are as follows : 1) The concentrations of cyclic AMP were linearly increased from the 1st week to the 3rd week up to 8.l0x10(-5) pmoles/cell and 0.85 pmoles/mg of protein, which were found to be 2.88-fold and 1.73-fold larger than the those of the 1st week's cultivation. The concentrations of cyclic AMP then gradually decreased from the 3rd week to the 7th week of the cultured-lifespan. 2) The biosynthetic amount of protein was found to be 1.74x10(-5)mg/cell on the 1st weekand 9.51x10(-5)mg/cell on the 3rd week of cultivation. Values were gradually declined from the 3rd week to the 7th week of cultivation. In the present investigation, it is clear that the amount of protein content and the concentration of cyclic AMP in the cultured human melanocytes derived form the epidermis of human skin were vividly increased up to the 3rd week of cultivation. Thus, it might be suspected that the suitable time for the successful transplantation of cultured human melanocytes is around the 3rd week of cultivation.