The nonlinear interaction between two pulsed, Gaussian ultrasonic beams propagating through degassed and filtered water was studied. One beam had a center frequency of 3.5 MHz and a peak pressure amplitude (in the interaction region) of 450 kPa. The other possessed a center frequency and peak pressure amplitude given by 3.0 MHz and 320 kPa, respectively. With the axes of the beams intersecting perpendicularly in the near-field, no sum-frequency scattered pressure amplitude greater than 0.03 Pa was detected outside the interaction region. The insertion of a brass sphere into the center of the interaction region resulted in the generation of two partially collinear scattered beams, and a sum-frequency scattered signal level of 0.9 Pa was subsequently detected at a 45±0.5° scattering angle. Experiments with collinear beams generated using a single projector driven by two electrically summed tone bursts (center frequencies=3.0 and 3.5 MHz) indicate the production of sum and difference frequencies in quantitative agreement with Westervelt’s theory for the parametric end-fire array [J. Acoust. Soc. Am. 32, 934A (1960)]. [Work supported by APL IR Funds.]