Several known antiallergic agents, including cromolyn sodium and a series of pyrido[2,1-b]quinazolines, inhibit human alkaline phosphatase (ALP), a membranal enzyme associated with calcium uptake in certain tissues. A comparison of ALP and rat passive cutaneous anaphylaxis (PCA) inhibition indicates that PCA inhibition may be associated with drug-ALP interaction, since ALP inhibition potency parallels PCA inhibitory activity. The unpredictability of the PCA test toward clinical efficacy could in part be related to the uncompetitive nature of these inhibitors. The results also suggest that alkaline phosphatase may be a component of membranal calcium channels.