Ultrasonic attenuation coefficients of liver have been derived from echoes received by a modified commercial B-scan imaging instrument. Values have been measured from selected regions within liver scans of 59 individuals, of which 15 cases were presumed normal (based on medical histories), and the remainder were involved with diffuse liver disease such as alcoholic cirrhosis, chemotherapy toxicity, chronic hepatitis, and liver metastases. Medical histories on most individuals include the results of serum liver function enzymes, conventional B-scan examinations, and exposure to drugs and alcohol. The results of CT abdominal scans (N = 13) and/or liver biopsy (N = 12) were also available. The results show that normal attenuation values for human liver are 0.054 +/- 0.009 Np/cm-MHz (0.47 dB/cm-MHz) with a frequency dependence of fn, where n = 1.05 +/- 0.25, in agreement with in vitro studies of mammalian liver. In diffuse liver disease, no relationship was found between the attenuation coefficient and the results of CT or conventional ultrasonic examination. A trend towards higher attenuation with increased fibrosis and fat, as graded from liver biopsies, was noted, but the results were generally not statistically significant. However, a significant correlation was found between high values of attenuation and abnormal liver function tests. High attenuation is also found with ingestion of alcohol, chemotherapeutic agents, and steroids, all of which may affect liver composition.