Starting from two weakly active hits from high throughput screening, a novel series of 2-(alkylthio)-pyrimidin-4-ones with high potency and selectivity for lipoprotein-associated phospholipase Az has been designed. In contrast to previously known inhibitors, these have been shown to act by a non-covalent and substrate competitive mechanism. (C) 2000 Elsevier Science Ltd. All rights reserved.