Completing the molecular analysis of the six pal genes of the ambient pH signal transduction pathway in Aspergillus nidulans, we report the characterization of palC and palH. The derived translation product of palH contains 760 amino acids with prediction of seven transmembrane domains in its N-terminal moiety. Remarkably, a palH frameshift mutant lacking just over half the PalH protein, including almost all of the long hydrophilic region C-terminal to the transmembrane domains, retains some PalH function. The palC-derived translation product contains 507 amino acids, and the null phenotype of a frameshift mutation indicates that at least one of the C-terminal 142 residues is essential for function. Uniquely among the A. nidulans pH-signalling pal genes, palC appears to have no Saccharomyces cerevisiae homologue, although it does have a Neurospora crassa expressed sequence tag homologue. In agreement with findings for the palA, palB and palI genes of this signalling pathway, levels of the palC and palH mRNAs do not appear to be pH regulated.