A series of substituted analogues based on the novel 2,3-dihydro-6-hydroxypyrimido[2,1-f]purine-4,8(1H,9H)-dione ring system have been synthesized and shown to exhibit antiinflammatory activity in the adjuvant-induced arthritis rat model (AAR). The activity exhibited by the pyrimidopurinediones in this model of chronic inflammation is comparable to that of their previously studied 2-oxo congeners, the 6-hydroxypyrimido[2,1-f]purine-2,4,8-(1H,3H,9H)-triones, the best of which show potency levels approximately equal to that of naproxen. On the basis of its potency in the AAR assay, 9-benzyl-2,3-dihydro-1,3-dimethyl-6-hydroxy-7-(3-methyl-2-butenyl) pyrimido-[2,1-f]purine-4,8(1H,9H)-dione was selected for further evaluation and found to exhibit cyclooxygenase inhibitory activity in the in vitro rat neutrophil model. With respect to side-effect liability, this prenylated derivative has been shown to be devoid of gastric ulcer inducing potential, as well as the ocular toxicity observed previously with the 2-oxo series.