Using the Chinese hamster V79 in vitro cell system designed to measure intercellular communication, 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and several mixtures of these compounds were tested for their ability to inhibit this biological process. The ability of these chemicals to inhibit colony-forming ability of these cells was tested prior to the studies to measure intercellular communication. 2,4-D was less cytotoxic than 2,4,5-T. Both 2,4,5-T and 2,4-D were able to inhibit intercellular communication at their respective noncytotoxic dose ranges. Various mixtures of both chemicals were also able to inhibit intercellular communication, showing some kind of additivity. No-effect levels were also noted in the intercellular communication assay. These results were interpreted as being consistent with the hypothesis that these compounds might be teratogenic by their ability to inhibit intercellular communication during development.