The relationship between depot formation and immunopotentiation was studied by comparing the retention of antigen at the inoculation site with antibody production in rats. A model ¹¹¹In-labeled alpha casein (IDCAS) antigen was formulated into four vaccines: IDCAS adsorbed onto either aluminum hydroxide adjuvant (AH) or aluminum phosphate adjuvant (AP); non-adsorbed IDCAS with phosphate-treated AP (PTAP); and IDCAS solution. Gamma scintigraphy showed the order of retention following subcutaneous administration to be: AH adsorbed>AP adsorbed>non-adsorbed with PTAP=solution. The antibody titers followed the order: non-adsorbed with PTAP=AP adsorbed>AH adsorbed≫solution. The presence of an aluminum-containing adjuvant was essential for immunopotentiation, but retention of the antigen at the inoculation site was not required.