Three patients with portal venous gas (one with radiographic and computed tomographic findings) had similar sonographic and Doppler patterns in the portal vein (PV). These patterns consisted of hyperechogenic foci moving within the lumen of the PV, producing sharp bidirectional spikes superimposed on the usual Doppler tracing of the PV. An injection of 0.25-0.50 cm3 of air, oxygen, nitrogen, and carbon dioxide into the jejunal vein of nine dogs yielded identical portal venous sonographic and Doppler patterns. In addition, the liver parenchyma of the dogs became hyperechogenic after the injection of gas. Gas in the PV is accompanied by the following signs: echogenic, moving foci within the lumen of the PV; sharp spikes on Doppler spectral display; and hyperechogenic foci within the liver parenchyma.