The effects of simultaneous active immunization against two cardiac glycoside drugs, digoxin and proscillaridin, have been examined in young spontaneously hypertensive and Wistar-Kyoto rats. Control animals were immunized with protein carrier only. Animals were studied from 5 weeks to 13 weeks of age. Effectiveness of immunization to produce antibody responses was assessed at the end of the study by estimating the titer of antibodies in plasma against both of the antigens. Robust antibody responses were obtained. Immunization had no effect on the normal growth of these animals. Further, immunization against cardiac glycosides did not change blood pressure in either strain of animals. Blood pressure in the SHR increased as anticipated as the weanling animals grew to maturity. These studies indicate that active immunization against cardiac glycosides does not alter blood pressure in the SHR in spite of strong evidence for increased levels of endogenous cardiac glycosides in this strain.