The effect of an extracellular neutral- and phosphopolysaccharide produced by Lactobacillus delbrueckii ssp. bulgaricus OLL 1073R-1 on macrophage functions was examined in short-term studies. The total number of peritoneal macrophages elicited by an intraperitoneal injection of 100 mg kg-1 of the polysaccharide was three fold greater than that by PBS. The macrophage phagocytosis was augmented by the phosphopolysaccharide in vivo and in vitro, but not or less by the neutral polysaccharide. The cytostatic activity of thioglycolate-induced macrophages against tumour cell lines (Sarcoma-180 or P388) was significantly augmented by a 6-h treatment of the phosphopolysaccharide at a concentration of 10-100 μg ml-1, while only at 100 μg ml-1 of the neutral polysaccharide. The phosphopolysaccharide purified by high performance liquid chromatography also had a substantial effect on macrophage cytostatic activity. The partial hydrolysis by trifluoroacetic acid treatment and dephosphorylation by hydrofluoric acid degradation of phosphopolysaccharides reduced the cytostatic activity in macrophages. The phosphopolysaccharide produced by Lactobacillus delbrueckii ssp. bulgaricus 1073R-1 is a potent enhancer of macrophage functions in which the conformational structure or phosphate group may play an important role. (C) 2000 Academic Press.