A newborn baby girl had a diffuse vasculitic rash and mild hepatosplenomegaly. Her birthweight was 2·6 kg and her parents were healthy and unrelated. Prenatal screening for rubella, cytomegalovirus, toxoplasmosis, herpes, and HIV was reportedly negative. Blood tests showed increased transaminases. In May, 2000, at the age of 3 months, she was referred to us with a persistent rash (figure), stunted growth, and loss of appetite. Her weight was 4·020 kg. We examined her and found massive hepatosplenomegaly and hypotonia. Blood tests showed thrombocytopenia, anaemia, and increased lactate deyhdrogenase (LDH); 1729 U/L (84–362) and ferritin; 1219 ng/mL (7–85). Immunofluorescence of Hep2 cells showed antinuclear antibodies (ANA) at a titre of 1:320 with a speckled pattern. Extractable nuclear antigen profile showed antiRo-SSA, and Coombs’ test was negative. We suspected that the child had neonatal systemic lupus erythematosus. However, an ECG did not show any abnormalities, 1 and the mother had no ANA or anti-RoSSA/La-SSB antibodies. This finding was confirmed with two additional different assays. A bone marrow aspiration showed haemophagocytic lymphohistiocytosis. Because of the presence of hepatosplenomegaly, poor feeding, muscular hypotonia, high levels of ferritin and LDH, we then considered the diagnosis of lysinuric protein intolerance (LPI, McKusick 22700). We measured plasma and urine concentrations of lysine, arginine, and ornithine. All three aminoacids were below normal levels in the plasma, and above normal in the urine. We also measured high levels of orotic acid in a 24 h urine collection. The diagnosis of LPI was confirmed by molecular analysis of the SLC7A7 gene. 2