The in vivo effect of one of aliphatic 2-ketones (undecan 2-one, further named U2one) on various parameters of specific and non-specific immunity in mice were studied. The activation of respiratory burst, measured by colorimetric assay (RBA) and activation of phagocytic activity of granulocytes (PKA test), as well as increased blood and splenic lymphocytes response to LPS and ConA were observed in mice inhaled with U2one for 3 days, 5 drops for 5 mice during 1 hour daily. In mice which inhaled this for 3 days after immunisation with sheep red cells (SRBC) significant stimulation of antibody response was observed on the day 7-th. F1 hybrid mice inhaled for 3 days (days 0, + 1 and +2) after intradermal grafting of parental cells presented on the 3-rd day significantly more newly-formed blood vessels (immunological angiogenesis) than respective controls. Serum lysosyme level increased in these mice, serum levels of C-reactive protein (CRP), gamma-globulins and ceruloplasmin did not differ from the controls