To investigate the interaction between tumor promoters and their cellular targets, 6 new fluorescent derivatives of indole alkaloid tumor promoter teleocidin were synthesized from (-)-indolactam V, and examined for induction of Epstein-Barr virus, binding ability to the TPA receptor on mouse skin and activation of protein kinase C. (-)-7-(2-N-Dansylaminoethyl)indolactam V (dansyl-ILV) had strong activities and proved to be a potent tumor promoter in a 2-stage carcinogenesis experiment. (-)-2-Formyl-7-decanoyl-indolactam V (FD-ILV) showed a weak but significant activity. The other 4 derivatives had little activity. Treatment of HeLa cells with dansyl-ILV and FD-ILV resulted in intense fluorescence in the entire cytoplasm and on the nuclear membrane. Inactive or less active derivatives with hydrophobicity similar to that of dansyl-ILV showed significant cytoplasmic fluorescence, and those far less hydrophobic than dansyl-ILV or far more hydrophobic than FD-ILV showed little fluorescence. This suggested that hydrophobicity rather than biological activity determines the cellular uptake of these fluorescent probes.