We examined the 3-amino-1,4-dimethyl-5H-Pyrido-[4,3-b]indole (Trp-P-1) concentration in the blood after administering Trp-P-1 (0.25 mg/ml) with or without Streptococcus thermophilus 1131 cells (10 mg/ml) to rats. The Trp-P-1 concentration in the blood from the portal vein was significantly lower in the rats that had been administered with Trp-P-1 with the strain 1131 cells than without them. However, there was no difference in the Trp-P-1 concentration in the blood taken from the abdominal aorta of these rats.