Potassium titanyl phosphate (KTiOPO4,KTP) has been used to generate blue 459-nm radiation by intracavity sum frequency mixing of the circulating 1064-nm laser radiation of a miniature neodymium:yttrium aluminum garnet laser and the 809-nm radiation used as the pump source. A blue output power of approximately 1 mW cw was obtained using 275 mW of pump power from an infrared dye laser. Gain-switched operation leading to high 459-nm peak powers was demonstrated. Direct rapid modulation of the blue radiation was achieved by modulating the pump. In preliminary experiments a high-power laser diode was used as the pump source for the generation of blue radiation.