4-undecanone (4-on) was used as the starting material in the synthesis of undecan-4-ol (4-ol) and 4-undecanone ethylene and propylene acetals (Acet4 and Acpr4). The in vivo effects of these substances on cellular and humoral immunity and on the syngeneic Sarcoma L-1 tumor growth were studied in inbred Balb/c mice and BDF1 hybrids. Mice were subjected to inhalation for three days. An increase of antibody production in mice which inhaled 10% 4-ol, 1% Acet4 or 1% Acpr4 were observed. The effect of 4-ol on cellular immunity(local graft-versus host reaction)depended on the scheme of experiment: was stimulatory when BDF1 recipients mice were inhaled after Balb/c donors lymphocytes grafting, and inhibitory when recipients obtained cells from inhaled parental Balb/c mice. However, when BDF1 hybrids were grafted with lymphocytes obtained from inhaled BDF1 donors, stimulatory effect was observed. No effects of inhaled 4-on were observed.. Intracutaneusly grafted Sarcoma L-1 tumors were significantly smaller in mice inhaled 4-ol, Acet4 and Acpr4 than in mice inhaled 4-on as well as those from the control group.