Effect of a series of 1-phenylthioureas 1a–k and 1, 3-disubstituted thioureas 2a–k were evaluated against melanin formation in melanoma B16 cell line and mushroom tyrosinase. Inhibitory activity of tyrosinase of 1-phenylthioureas 1a–k is parallel to their melanogenic inhibition. Thus, the melanogenic inhibition in melanoma B16 cells of 1-phenylthioureas could be the result of inhibition of tyrosinase. However, 1, 3-diaryl or 1-phenyl-3- ...