The mycotoxin fumonisin is associated with oesophageal cancer and birth defects. The Eastern Cape province of South Africa has high levels of fumonisin in maize and oesophageal cancer. This study measures the amounts of the mycotoxin fumonisin in the grain of Bt maize, commercial hybrids, and farmer-saved, local mixtures of seed that were produced and stored by small holders in South Africa. We find that adoption of Bt maize can reduce poor rural consumers exposure to fumonisin. Greater consumption of maize meal milled in modern mills could have a similar impact.