Abstract: Methods of inhibiting phosphatidylinositol 3-kinase delta isoform (PI3K&dgr;) activity, and methods of treating diseases, such as disorders of immunity and inflammation, in which PI3K&dgr; plays a role in leukocyte function are disclosed. Preferably, the methods employ active agents that selectively inhibit PI3K&dgr;, while not significantly inhibiting activity of other PI3K isoforms. Compounds are provided that inhibit PI3K&dgr; activity, including compounds that selectively inhibit PI3K&dgr; activity. Methods of using PI3K&dgr; inhibitory compounds to inhibit cancer cell growth or proliferation are also provided. Accordingly, the invention provides methods of using PI3K&dgr; inhibitory compounds to inhibit PI3K&dgr;-mediated processes in vitro and in vivo.