Water-in-oil-type adjuvants prepared with natural or synthetic vitamin E as the oil phase, Arlacel A or Montanide 103 as emulsifier and 1.0% aqueous solution of bovine serum albumin (BSA) as antigen were tested in mice. An emulsion of 0.42 ml vitamin E, 0.42 ml special mineral oil, 0.15 ml Arlacel A and 1.0 ml BSA gave maximal humoral response, but 0.85 ml special mineral oil, 0.15 ml Arlacel A and 1.0 ml BSA (standard Freund's incomplete adjuvant formulation) gave the greatest delayed-type hypersensitivity response.