1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) in concentrations from 0.1 to 10 nM suppressed immunoreactive thromboxane B2 (iTXB2) release from Propionibacterium acnes (P. acnes)-elicited liver adherent cells stimulated with lipopolysaccharide (LPS, 1 microgram/ml). These suppressive effects of 1,25-(OH)2D3 were also observed in oyster glycogen-elicited peritoneal macrophages. On the contrary, it did not inhibit iTXB2 release from both resident Kupffer cells and peritoneal macrophages stimulated with the same concentration of LPS. Furthermore, 1,24(R)-dihydroxyvitamin D3 (1,24(R)-(OH)2D3), a vitamin D3 analogue, also inhibited iTXB2 release from liver adherent cells, but, another synthesized vitamin D3 analogue, 1 alpha-hydroxyvitamin D3 (1 alpha-OH-D3) tended to decrease iTXB2 release only at higher concentrations. These results suggest that active vitamin D3 analogues inhibit iTXB2 release from activated macrophages.