In our 3 years of clinical experience, we have found that diagnostic ultrasound provides the veterinarian with a valuable diagnostic tool. It allows the clinician to quantify morphologic change that has occurred as a result of soft-tissue injuries, even when the clinical findings are ambiguous or insufficient. In cases in which aggressive postinjury therapy has been instituted prior to presentation, diagnostic ultrasound is often the only noninvasive method that can ascertain the extent of the horse's injury. Diagnostic ultrasound provides the technology to detect injuries before they become permanently debilitating, because lesions as small as 1 mm in diameter can be detected. Prior to diagnostic ultrasound, the severity of many injuries was underestimated. In such cases, if the horse responded favorably to symptomatic therapy, the client would resume training. The result was often debilitation. Diagnostic ultrasound also enables the clinician to demonstrate visually to the client the location, size, and extent of lesions in the limb. One of the more gratifying effects of a sonographic study is the client's acceptance of the presence and extent of the injury after visualizing it. We have found that the old adage "a picture is worth a thousand words" is generally the rule in obtaining the proper course of therapy for the horse. The ability to make hard copies of sonograms enables the clinician to morphologically evaluate the rate of healing. He can accurately determine the effectiveness of a therapeutic regimen and ascertain when optimal healing has occurred. Diagnostic ultrasound can provide the researcher with an invaluable tool to document and quantify soft-tissue disease. We anticipate that, in the future, the sonographic appearance of recovered tissues will be correlated with new data on the healing process and the effectiveness of various therapies. The material presented above has covered the value of diagnostic ultrasound in major clinical situations related to equine lameness. Other applications, the discussion of which is beyond the scope of this article, include evaluation of the pastern for injuries to the SDF, DDF, and oblique sesamoidean ligament, and evaluation of the navicular bursae. Examination of muscles for hematomas, abscessations, and tears has also been accomplished ultrasonographically. Diagnostic ultrasound has facilitated study of the trochanteric and bicipital bursae, blood flow through arteries, and structures above the carpus and hock. Obviously, the clinical potential of diagnostic ultrasound is limitless.(ABSTRACT TRUNCATED AT 400 WORDS)