This report describes a new disorder resembling hereditary tyrosinemia (HT) but differing from it in several respects. Similarities include failure to thrive with hypoproteinemia, micronodular cirrhosis, alpha-fetoprotein positive hepatocellular carcinoma, renal Fanconi syndrome with renal tubular ectasia, hypermethioninemia, and hypoglycemia associated with islet cell hyperplasia. However, the tyrosine metabolic pathway was intact. Unique findings include optic atrophy, cerebellar degeneration, and exocrine pancreatic hypoplasia. Polyunsaturated fatty acid (PUFA) status was evaluated in the serum and liver. Initial PUFA profile to serum phospholipids revealed grossly elevated linoleic acid and subnormal linolenic acid. All PUFAs derived from these precursors were absent suggesting gross abnormalities in the utilization of these two essential fatty acids for synthesis of longer chain highly unsaturated structural PUFA. Analysis of liver phospholipids indicated that linoleic acid was lower and w3 and monenoic acids were higher than in the liver specimens from two cases of HT. The gross abnormalities in PUFA pattern, although perhaps secondary to another cause, represent serious structural and functional abnormalities of essential membrane lipids and potentially of eicosanoids derived from them.