Spin-polarized nuclei of such gases as 3He and 129Xe are successfully used for magnetic resonance imaging of lungs and other organs of human body. To produce large numbers of spin-polarized nuclei required for this medical application, a high power narrowband tunable laser source is required. Diode pumped alkali lasers, developed during last several years can be an ideal source for this application. In this paper we present our latest achievements in diode pumped alkali lasers development. We describe optically pumped Cs laser tunable in the range of 14 GHz and operating in single transverse mode with a linewidth less than 3 MHz. We also present continuous wave diode pumped Rb and Cs lasers with output power 17 W and 20 W.