An experimental study of drop formation at the free surface of plane turbulent jets in gases (i.e., turbulent primary breakup) is described. Test conditions consisted of fully-developed turbulent plane water jets injected into still air at standard temperature and pressure with Reynolds numbers of 91,000-424,000, Weber numbers of 13,000-151,000 and Ohnesorge numbers of 0.0009-0.0012. Pulsed shadowgraphy was used to measure mean liquid surface velocities, mean and fluctuating drop velocities after primary breakup, drop sizes after primary breakup and the location of the onset of primary breakup. Drop velocities were related to the average streamwise velocity in a relatively simple manner, while drop size properties could be related to earlier findings for turbulent primary breakup of round liquid jets in still gases using hydraulic diameter concepts.