A series of amide derivatives of long-chain fatty acids has been studied for their effects on the proliferation of cancer cells in vitro. Fatty acids ranged from palmitic to higher polyunsaturated types containing 22 carbon atoms. The amino portions of the molecules included ammonia, ethanolamine, various amino acids and dopamine. Several cell lines were used as models and these included HTB-125 (normal human breast cells), HTB-126 (human breast cancer cells), HeLa (cervical cancer cells), WI-38 (human embryonic lung cells), RAW264.7 (mouse macrophage tumor cells) and RBL-2H3 (rat basophilic leukemia cells). The HTB lines were obtained from the same donor, so, could be considered a matched pair, that is, normal control versus cancer cells and thus, provide a model for testing specificity of action for the acylamido analogs. While many compounds were efficacious in inhibiting the proliferation of various cell lines, only two analogs showed a high degree of specificity in the matched HTB cell lines. N-palmitoyl dopamine and N-palmitoyl tyrosine each demonstrated complete specificity of action at a concentration of 10muM and were highly efficacious in both cases. No clear structure-activity pattern could be derived from these studies since the intensity of the inhibitory action seemed to depend on three factors, namely, the fatty acid, the amine group and the cell type.