A sensitive method was developed for the determination of deoxynivalenol (DON), nivalenol (NIV),α‐zearalenol (α‐ZEL),β‐zearalenol (β‐ZEL) and zearalenone (ZEN) in beer by capillary gas chromatography‐mass spectrometry (GC‐MS) of their heptafluorobutyrate (HFB) derivatives. Recoveries averaging 90–103% were obtained from beers spiked with each mycotoxin in the 5–20 ng/ml concentration range. Limits of detection were 0.1–1.5 ng DON/ml, 0.01–0.3 ng NIV/ml, 2.5–3 ngα‐andβ‐ZEL/ml, and 1.5–2 ng ZEN/ml. Twenty‐nine of 50 samples of Canadian and imported beer surveyed were found to contain DON; of these nine contained greater than 5 ng/ml (up to 50 ng/ml). The identity of DON was confirmed by response ratios atm/z670 andm/z884 for the HFB derivative andm/z497 andm/z512 for the trimethylsilyl (TMS) derivative. NIV was also detected in three beer samples (0.1–0.84 ng/ml) but no α‐ZEL,β‐ZEL or ZEN was found