Preliminary results of in vivo attenuation measurements of the liver have been obtained in 39 normal patients and in 35 patients with diffuse liver disease. A modified real-time sector scanner incorporating an online attenuation measurement method was used. The value of attenuation in normal liver was estimated as 0.52 +/- 0.03 dB/cm/MHz, measured at 3 MHz. Significantly higher attenuation values were obtained from patients with alcoholic and cardiac cirrhosis, and following hepatic artery infusion with chemotherapeutic agents. Lower values were obtained from patients with biliary cirrhosis, chronic active hepatitis, and diffuse infiltration by lymphoma or leukemia. Fatty infiltrated livers showed a wide range of values of 0.37-0.66 dB/cm/MHz. The results suggest that estimates of attenuation coefficients are useful in detecting the presence of diffuse liver disease.