Injections of kynurenine (10 and 25 mg/kg, i.p.) and nicotinic acid (50 mg/kg i.p.) produced a marked increase in concentration of 11-hydroxycorticosteroids (11-HCS) in rat blood plasma. Effect of nicotinic acid was not prevented by dexamethazone (0.6 mg/kg). Subtreshold dose of nicotinic acid (10 mg/kg) enhanced a rise in 11-HCS produced by swimming stress. 3-hydroxykynurenine, 3-hydroxyanthranilic, antranilic picolinic and quinolinic acids (10-50 mg/kg) did not change the concentration of 11-HCS. It is suggested that some of the biochemical and pharmacological effects of injected kynurenine can be mediated through the rise of 11-HCS in blood.