Spatial inhomogeneities in the acoustic velocities of tissues distort propagating wave fronts and degrade the quality of diagnostic ultrasonic images. A real-time adaptive ultrasonic imaging system has been developed that uses image quality factors to iteratively adjust the phasing of transducer elements and restore image quality. This system has been used to evaluate a number of alternative quality factors and iterative algorithms for diffuse reflectors, pointlike targets and clinical targets, and good success with such targets was achieved with image-brightness based quality factors. The results of these experiments agree well with theoretical descriptions of adaptive imaging and with direct measurements of the characteristics of phase aberrations in human tissues.