Technical Abstract: Maize samples (n=396) were collected from fields in Guatemala from 2000 to 2003. Maize from the lowlands (< 360 m) had significantly more fumonisin than highland maize (>1200 m). Approximately 78% of the lowland samples collected at harvest in 2002 contained >0.3 ug/g of fumonisin B1, whereas, only 2% of the samples collected at harvest from the highlands during the same year contained >0.3 ug/g. However, maize collected from storage in the highlands contained significantly more fumonisin B1 compared to the levels at harvest in 2002. All of the Fusarium infected kernels analyzed from nine random lowland locations were infected with F. verticillioides and no other Fusarium species, whereas, in samples from the highlands only 5% of the Fusarium positive kernels were F. verticillioides. All of the F. verticillioides isolates produced fumonisin in culture. In 2005, maize samples (n=236) from the 2004 crop were collected from local markets in 20 Departments across Guatemala. The analysis showed that maize from lowland locations was often highly contaminated with fumonisin and was frequently sold in highland markets. Thus, fumonisin exposure in the highlands will be greatest in groups that obtain their maize in the market place from commercial vendors. Based on a recall study and published consumption data, a preliminary assessment of daily intake of total fumonisins was estimated. Consumption of nixtamalized maize products made from over 50% of the maize from commercial vendors in 2005 could result in exposure exceeding the recommended World Health Organization provisional maximal tolerable daily intake.