The ability of orally administered Deodan, a product from the cell wall of Lactobacillus bulgaricus strain "I. Bogdanov patent strain tumoronecroticance B51" ATCC #21815, shortly called "LB51", to induce endogenous tumor necrosis factor-alpha (TNF alpha) production in normal mice was evaluated. The priming and triggering activities of the preparation were investigated in combination with lipopolysaccharide (LPS) and live BCG vaccine. Deodan was applied at a dose of 150 mg/kg and various treatment schedules were employed. The serum levels of TNF alpha in treated mice were quantified by ELISA. Oral administration of Deodan at a dose of 150 mg/kg for 1, 3, 10 or 20 consecutive days only enhanced serum TNF alpha levels in treated mice. Maximal TNF alpha levels were reached 6 h after the last application of Deodan. Deodan was effective in priming TNF alpha in mice triggered intravenously (i.v.) with LPS. Deodan triggered the production of TNF alpha in BCG-primed mice. The preparation, however, was not an effective trigger of mice primed intradermally (i.d.) with 1 microgram/mouse LPS. These findings suggest that Deodan is both a primer and trigger of endogenous TNF alpha. The advantages of treatment of neoplastic disease with agents which induce endogenous TNF alpha is discussed.