Natural mycoflora and fumonisins were analysed in 490 samples of freshly harvested corn (Zea mays L.) (2003 and 2004 crops) collected at three points in the producing chain from the Northern region of Parana State, Brazil, and correlated to the time interval between the harvesting and the pre-drying step. The two crops showed a similar profile concerning the fungal frequency, and Fusarium sp. was the prevalent genera (100%) for the sampling sites from both crops. Fumonisins were detected in all samples from the three points of the producing chain (2003 and 2004 crops). The levels ranged from 0.11 to 15.32 microg g(-1)in field samples, from 0.16 to 15.90 microg g(-1)in reception samples, and from 0.02 to 18.78 microg g(-1)in pre-drying samples (2003 crop). Samples from the 2004 crop showed lower contamination and fumonisin levels ranged from 0.07 to 4.78 microg g(-1)in field samples, from 0.03 to 4.09 microg g(-1)in reception samples, and from 0.11 to 11.21 microg g(-1)in pre-drying samples. The mean fumonisin level increased gradually from < or = 5.0 to 19.0 microg g(-1)as the time interval between the harvesting and the pre-drying step increased from 3.22 to 8.89 h (2003 crop). The same profile was observed for samples from the 2004 crop. Fumonisin levels and the time interval (rho = 0.96) showed positive correlation (p < or = 0.05), indicating that delay in the drying process can increase fumonisin levels.