Zearalenone (ZEA), an oestrogenic secondary metabolite of Fusarium, is a common feed contaminant. Lactic acid bacteria are capable to bind ZEA and this property could be used to limit its negative biological effects on farm animals. The aim of this work was to examine the stability of a lactic acid bacterium, Streptococcus thermophilus RAR1-ZEA complex in ruminal fluid and in conditions simulating compartments of the gastrointestinal tract. The lactic acid bacteria-ZEA complex was 70% stable in ruminal fluid incubations for up to 18 h, and about 50% of ZEA initially complexed still remained bound after incubation in pepsin, lysozyme, pancreatin and bile either alone or sequentially. However, the release of ZEA was predominantly caused by washing, except for bile which produced a partial dissociation of the complex (P<0.05). Addition of free ZEA to ruminal fluid resulted in instantaneous binding of about 70% of the toxin. ZEA bound to ruminal fluid was even more stable than lactic acid bacteria-ZEA in in vitro ruminal fermentations and in simulated gastrointestinal tract juices. It is concluded that complexation of ZEA in ruminal fluid could help protect ruminants against the toxin, and that the use of selected strains of lactic acid bacteria efficiently binding ZEA to limit its toxic effects could be more advantageous in monogastric animals.