In several publications, Müller and Myers1 have postulated a stimulation of the autonomic nervous system, principally the parasympathetic division, after the intravenous injection of arsphenamine. This stimulation, they claim, is increased in persons responding with undesirable reactions, or "nitritoid crises." The sole basis for their claims is a temporary leukopenia, which is somewhat more marked and lasting (about twenty to fifty minutes) during the "nitritoid crisis." In support of their claims they cite analogous leukopenias occurring after the intradermic injection of nonspecific agents, such as proteins and 0.9 per cent sodium chloride, and after strong stimulation of the skin, from which they claim further a reflex stimulation of the autonomic nerves. These authors apparently assume that an acute leukopenia is the equivalent of parasympathetic (autonomic nerve) stimulation. A priori, this premise appears to be false, and, in any case, the evidence of parasympathomimetic action of arsphenamine is wholly lacking,