Striped bass inhabiting Lake Keystone, Oklahoma, spawn in a 150-km long reach of the Arkansas River below Kaw Dam. We sampled ichthyoplankton in this reach from mid-March through May in 1987 and 1988 to determine when and where striped bass spawning occurred. Collections were made twice weekly with conical plankton nets fished just below the surface from 4 bridges and by boat in the Kaw Dam tailwater. Spawning was initiated in mid-April of both years at water temperatures of 11.8°-14.9° C, peaked in late April to early May at temperatures of 15.0°-22.3° C and terminated in mid-May when water temperatures were 25.3°-27.5° C. Peak densities of striped bass eggs generally increased with distance (to about 50 km) from Kaw Dam. Striped bass spawning was concentrated near the confluence of the Salt Fork and Arkansas rivers, where discharges and water temperatures increased abruptly.