Recent improvements in ultrasound technology, including spectral Doppler and color flow imaging, have significantly expanded the applications of ultrasound in the liver. Intravenous ultrasound contrast agents may have a role in overcoming current difficulties in the sonographic detection and characterization of tumors and low-velocity flow vessels, by increasing the reflectivity of blood in small, deep vessels. Intravenously administered, echo-enhancing microbubbles suspended or encapsulated in various carrier materials provide stability and prolonged enhancement of the Doppler signal. Numerous studies have demonstrated that contrast-enhanced Doppler ultrasound has promise in the detection of hepatocellular carcinomas and their differentiation from benign lesions, such as focal nodular hyperplasia, hemangiomas, and focal fat. Contrast enhancement may also improve the visualization of vascular abnormalities associated with chronic liver disease. In addition, gray-scale enhancement may improve the detection of hepatic tumors. The technique of harmonic imaging will likely further improve the contrast-enhanced visualization of the liver and hepatic vessels. With the availability of contrast agents, particularly those capable of producing prolonged enhancement, sonography may expand its unique advantages over other techniques in the diagnosis and management of hepatic diseases. Contrast-enhanced ultrasound may decrease the need for correlative imaging and offers an alternative for patients with iodine-contrast allergies or those who cannot undergo MRI.