Induction of transglutaminase was analyzed based on increases in the maximal enzymic activity and in the Northern blots of mRNA during culture of mouse resident peritoneal macrophages with active forms of hydrophobic vitamins and steroid hormones. The enzyme was induced by 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25-(OH)2D3) or retinoic acid but not by steroid hormones. The induction by 1 alpha,25-(OH)2D3 was characterized by its slow onset and marked synergism with retinoic acid induction. The induction was enhanced by protein kinase activators such as cholera toxin and phorbol 12-myristate 13-acetate but largely inhibited by pertussis toxin treatment of cells. It is suggested that pertussis toxin-linked and protein kinase-related signaling would mediate the 1 alpha,25-(OH)2D3-induced enzyme gene expression.