The expression of various connexins so far identified is metabolically and developmentally regulated. Examples include uterine endometrium where the expression of gap junction protein, connexin32 (Cx32) is regulated by steroid hormones. In this study we attempted to synthesise a short peptide which matches the portion of the amino acid sequence of the Cx32. Cx32 has primary structure predicted from the nucleotide sequence of cDNA clone. A fragment of Cx32 molecule was synthesised to produce anti-peptide antibody for detecting gap junction protein in mouse and rat liver and endometrium. The 12-peptide, plus Abu residue that corresponds to residues 108-119 (LEGHGDPLHLEE-Abu) of the rat Cx32 (283-mer) was synthesised by the solid phase method. Antibodies against this peptide were raised in rabbits, screened for reactivity and specificity using dot blot assays [15] and used for immunocytochemical staining at the light and at electron microscope levels. The antibodies also reacted with fish heart myocardium.