The fumonisin B-1 content of 69 visibly mouldy and 23 mould-free maize samples grown in Hungary in 1993-1995 was determined by high-performance liquid chromatography (HPLC). Fumonisin B-1 was found to occur in 70-73 % of the mouldy samples. The mycotoxin level increased from year to year: the highest fumonisin B-1 concentration was 75.1 mg/kg. The samples that were mould-free on visual inspection showed a much lower prevalence of fumonisin B-1 contamination (30%) and contained Fumonisin B-1 in markedly lower concentrations (average, 1.52 mg/kg; maximum concentration, 5.1 mg/kg). Using the Fusarium moniliforme strain designated 14/A, isolated from the sample that had the highest mycotoxin concentrations, fumonisin B-1 toxin was produced on maize br an internationally accepted procedure. Subsequently, two weaned piglets were fed a diet containing 330 mg fumonisin B-1 per kg of feed. The experimental animals developed hydrothorax and pulmonary oedema, and died in 5-6 days. The clinical symptoms and pathological lesions were consistent with those of porcine pulmonary oedema (PPE) diagnosed in the USA in 1989-1990, as well as with those of a disease entity that had already been described in Hungary in the 1950s as the so-called fattening or unique pulmonary oedema of pigs but considered to be of unknown aetiology. The results of the feeding trial confirm chat this pig disease, which has occurred in Hungary for a long time, is caused by the mycotoxin fumonisin B-1.