The productivity of wheat and corn crops depends on climatic conditions and resistance against phytopathogenic fungi such as those of the genus Fusarium. Some species of this genus produce zearalenone (ZEA), a mycotoxin with hyperestrogenic effects. The objective of this study was to investigate the presence of ZEA in samples of cracked wheat (n = 109), popcorn (n = 51) and corn grits (n = 50) commercialized in the State of Paraná, Brazil. Commercial samples of each crop were collected between September 2007 and June 2008 and analyzed by thin-layer chromatography. The method used for detection of the mycotoxin in wheat and corn derivatives presented a recovery rate of 94.5% and 99.5%, respectively, detection limit of 40 μg.kg-1 and quantification limit of 55 μg.kg-1. No contamination with ZEA was detected in cracked wheat samples. Among the corn derivatives, only one cracked corn sample was contaminated with ZEA (64 μg.kg-1). Despite the low contamination observed, monitoring the occurrence of mycotoxins in foods is important to ensure safety.