The hypocalcemic substance P-MSY (mol. weight 66,000) and a few partially purified products obtained by HOAc extraction of bovine parotid extract were examined for immune adjuvanticity.The P-MSY (0.1 μg/mouse) produced a lymphocyte/polymorphonuclear leukocyte (L/P) ratio of 2.72, and the effect was significant at 1% against the control group.Plaque + rosette-forming cell (PFC and RFC) activities were significant at <5% level of significance against the resp. control group in a dose of 2.5 μg/mouse (PFC/106 cells: 53.57, RFC/106 cells: 13,854).The L/P activity of P-MSY was increased by ∼2000 times that of Me2CO-dried powder PAI and starting materials, and the increases in PFC and RFC activities were both ∼80 times.Through the assay of P-MSY and partial purified products, a tendency to increase in L/P, PFC, and RFC activities was found in proportion to hypocalcemic activity.The regression of L/P and PFC activities against log doses were examined, and it was concluded that each response resolved linearly over a moderate range of doses.