It has been shown that portal hypertension in the rat causes microvesicular hepatocytic fatty infiltration. Formation of megamitochondria (MG) is one of the most prominent alterations in steatosis. Because nitric oxide (NO), tumor necrosis factor-α (TNFα), and interleukin-1β (IL-1β) impair mitochondrial function, these mediators have been studied in prehepatic portal hypertensive rats to verify their coexistence with MG and therefore with steatosis. Male Wistar rats were divided into two groups: a control group (n = 7) and a group with partial portal vein hgation (n = 19) at 6 weeks of evolution. TNFα and IL-1β were quantified in liver by enzyme-linked immunosorbent assay, and NO was measured in the portal vein, suprahepatic inferior vena cava, and infrahepatic inferior vena cava by the Griess reaction. In portal hypertensive rats, the-serum concentration of NO of hepatic origin increases (132.10 ± 34.72 vs. 52.44 ± 11.32 nmol/ml; p < 0.001), as do TNF-α (2.02 ± 0.20 vs. 1.12 ± 0.43 μmol/mg protein) and IL-1β (18.95 ± 2.59 vs. 5.48 ± 1.70 μmol/mg protein) (p = 0.005) in the liver. The most frequent hepatic histologic findings are the presence of MG (p < 0.001), steatosis, and hyperplasia. An increase in hepatic release of NO, TNFα and IL-Iβ with MG formation is produced in rats with portal hypertension. Therefore these proinflammatory mediators and this morphologic mitochondrial alteration could both be involved in the etiopathogenesis of steatosis.