AbstractThe influence of folic acid and several antagonists of the folic acid metabolism on neutrophil superoxide generation was investigated with the cytochrome c reduction assay. The compounds were found to be partial competitive inhibitors of the NADPH oxidase, their activity apparently increasing with larger substituents at the 10 position. There is evidence that compounds with a 4-oxo substituent are taken up more slowly by neutrophils than those with a 4-amino functionality. Scavenging properties could be excluded from control measurements with the xanthine/xanthine oxidase assay.