In a long-term study (1990-1997) on ochratoxin A (OTA) in human blood serum, 102 serum samples from 36 persons of the Munich Institute for Hygiene and Technology of Food of Animal Origin were analysed by enzyme immunoassay (EIA), and by high performance liquid chromatography (HPLC) for control. Detection limits were at 50pg/ml (EIA) and 50-70pg/ml (HPLC), recoveries were 80-120% (EIA) and 30-60% (LC). OTA was detected in 98% (EIA, 368 ± 217pg/ml) and 93% (HPLC, 271 ± 170pg/ml) of samples (maximum 1,290pg/ml). Using published conversion factors for serum/intake estimates (1.34 or 1.97), the mean daily OTA intake of these 36 persons was 493-725pg/kg bw. Long-term individual mean OTA levels of nine persons ranged from 162 ± 80pg/ml to 549 ± 172pg/ml. Our data were compared with published OTA serum levels (1985-2008) for apparently healthy persons from a total of 30 countries. On a worldwide basis, the mean of means for OTA in human serum was estimated to be 700pg/ml, corresponding to a mean daily OTA intake of 940-1380pg/kg bw. This level, which was relatively stable over the last decades, is well below published tolerable daily intake values (14,000-18,000pg/kg bw).