As part of our studies on pyrimidine derivatives, 27 4-alkyl-2-(1-piperazinyl)-5, 6-polymethylenepyrimidines and structurally related derivatives were synthesized, and their hypoglycemic activities were examined in mice treated with 2-deoxy-D-glucose. Most of the derivatives showed higher activity at a dose of 30 mg/kg p.o. than tolbutamide at a dose of 100 mg/kg p.o. The structure-activity relationships are discussed.