Clinical and laboratory observations are provided on high, spontaneous, in vitro histamine release (HSHR) from leucocytes (basophils), meaning without addition of antigen or other inducers of histamine release. HSHR has been observed predominantly in persons with a high degree of reaginic sensitivity to food; the leucocytes of forty-eight of fifty-eight individuals (83%), who had positive reactions to foods in double-blind challenges, exhibited HSHR. HSHR resembles antigenic release in a wide variety of characteristics. HSHR does not occur in vivo but only in vitro after compaction of leucocytes by centrifugation at room temperature. An indispensible requirement for HSHR to occur appears to be a high degree of reaginic sensitization.