The quantitative dose requirements for induction of paralysis by BSA in mice has been the subject of further study. Parallel studies have been made with lysozyme, ovalbumin, diphtheria toxoid and ribonuclease, in which similar paralysing and immunizing procedures were used, and similar direct binding tests applied to measurement of the response. In normal adults all the antigens tested induced high-zone paralysis and concomitant immunization, but BSA alone induced low-zone paralysis. With irradiation, with courses of injection commencing at birth, and with paralysis-maintaining treatment, all the antigens tested induced paralysis in a zone quantitatively similar to the low zone detectable in normal adults with BSA. Neither irradiation, treatment with cortisol, nor thymectomy affected the rate of induction of paralysis in the low zone. On the other hand the minimum dose required for immunization varied markedly from one antigen to another.