Gastrin conjugated to bovine serum albumin was administered to New Zealand white rabbits by repeated injections at a standard immunizing dose of 2 mg BSA-gastrin conjugate, as well as at 0.2 mg (10%) and 0.02 (1%) of BSA-gastrin conjugate. The immediate dose of immunogen (0.2 mg) was also given by multiple simultaneous intradermal injections, with one later booster immunization. Resultant antisera from footpad injected rabbits were found to be of comparable high affinity, which was uninfluenced by the size of the administered dose of antigen conjugate. Antibody binding sites concentrations in these antisera, however, were found to be proportional to immunizing dose. Antibodies to gastrin produced after intradermal injection, although of comparable serum antibody concentrations, were of significantly lower affinity than after footpad immunization. It is concluded that high affinity antisera suitable for use in radioimmunoassay of gastrin can be produced by footpad immunization utilizing a small fraction of the standard immunizing dose of gastrin-bovine serum albumin conjugate.