The synthesis of pyridopyrimidines, pyrazolopyrimidines, pyridothienopyrimidines, pyridothienotriazines and pyridodithienoditriazines and their evaluation as inhibitors or inducers of the release of histamine is reported. The activity was measured under immunological and chemical stimulus with polymer 48/80 and the drugs adryamicin and vinorelbine. The experiments were carried out with and without preincubation of the stimulus with the cells before addition of the drug. Their antitumor activity have been tested in vitro against standard P-388, A-549, HT-29 and MEL-28 tumor cell lines.