The phosphoinositide 3-kinase (PI3K) family of enzymes consists of several closely related isoforms that are thought to have distinct biological roles. Until now, researchers have been frustrated by poor selectivity of the available pharmacological inhibitors, which are unable to distinguish adequately the activities of different PI3K isoforms. Recently published patent specifications describe new PI3K inhibitors, including several that are selective for the PI3Kdelta isoform. There is now cautious optimism that isoform-selective PI3K inhibitors will provide new avenues for therapeutic applications in a range of diseases.