Six different types of antigens were prepared from Candida albicans viz. whole cell homogenate (CAD-G), partially purified soluble mannan (M ), particulate mannan adsorbed onto latex particles (M+L) , purified cytoplasmic protein (PP), culture filtrate (CF) and killed whole cells (WC) . The stimulatory effects of these antigens were tested on peripheral blood lymphocytes of 20 normal human subjects by in vitro lymphocyte transformation tests. The order of stimulation capacities was CF > CAD-6 >WC >M+L>PP >M. Thus the crude antigens were found to be superior to purified and soluble preparations in promoting lymphocyte transformation. The LD50 of test strain of C. albicans (NCPF 3153) to "TO" strain mic e was estimated and calculated to be 1.52 x 10^6 blastospores. Seven groups of mice were immunized with the same antigens and challenged subsequently with a lethal dose of 4 x 10^6 live organisms . Live cells of C. albicans were also used to immunize mice before challenge. The agglutinin titres of the immunized animals ranged from 1:4 to 1:64. The group immunized with killed whole cells of Candida had highest agglutinin titres. The precipitin reactions were directed principally toward CA0-6 and purified cytoplasmic protein antigens. Different antigens conferred different degrees of protection in the following order: CAD-6 > M+L>CF>PP>WC(A) = M>WC(K) Heat killed vaccine (WC(K)) did not confer any measurable protection. Surviving animals showed agglutinin titres which ranged from 1:4 to 1:16 and precipitins which were directed primarily against CAD-6 and PP antigens. None of the groups showed any anti-mannan precipitins. Mice immunized with heat-killed hole cells of C. albicans and control animals showed the same responses to thigh muscle challenge with 5 x 10^8 live organisms. An abscess was formed which resolved spontaneously after 4 weeks with a cellular reaction mostly of polymorphonuclear cells. Candida was present mostly in the mycelial phase . Repeated thigh muscle challenge with live organisms produced local resistance manifested by accelerated sequestration of abscesses and the appearance of Candida mostly in yeast phase.