A series of straight and branched chain phthalate monoesters were examined for their effects on hepatocyte intercellular communication in male B6C3F1 mouse hepatocytes. Intercellular communication was determined autoradiographically following the passage and incorporation of (5-(3)H)uridine nucleotides from pre-labelled hepatocytes into nonlabelled hepatocytes. Intercellular communication was evaluated in hepatocytes after 8 hours treatment of straight and branched chain phthalate esters at sublethal concentrations. Straight chain phthalate monoesters (mono(ethyl)phthalate, mono(n-butyl)phthalate, mono(n-hexyl)phthalate, mono(n-octyl)phthalate, mono(n-nonyl)phthalate and mono(isononyl)phthalate) had no effect on hepatocyte intercellular communication. Branched chain phthalate monoesters that contained an ethylalkyl moiety (mono(2-ethylpropyl)phthalate, mono(2-ethylbutyl)phthalate, mono(2-ethylpentyl)phthalate and mono(2-ethylhexyl)phthalate) inhibited intercellular communication. These results show a structure-activity relationship in the ability of phthalate monoesters to inhibit intercellular communication in mouse hepatocytes. Based upon previous correlations between inhibition of intercellular communication in hepatocytes and hepatocarcinogenicity, these data suggest that branched chain phthalate esters may be liver carcinogens in male B6C3F1 mice. (Copyright (c) 1988, Elsevier Scientific Publishers Ireland, Ltd.)