Fifty-two isolates of Fusarium species were obtained from soybean seeds from various parts of Korea and identified as Fusarium oxysporum, F. moniliforme, F. semitectum, F. solani, F. graminearum, or F. lateritium. These isolates were grown on autoclaved wheat grains and examined for toxicity in a rat-feeding test. Nine cultures were toxic to rats. One of these, a culture of Fusarium sp. strain KCTC 16677, produced apicidin, an antiprotozoal agent that caused toxic effects in rats (including body weight loss; hemorrhage in the stomach, intestines, and bladder; and finally death) when rats were fed diets supplemented with 0.05 and 0.1% apicidin. The toxin was toxic to brine shrimp (the 50% lethal concentration was 40 μg/ml) and was weakly cytotoxic to human and mouse tumor cell lines.