Lactobacillus paracasei subsp. tolerans, isolated from a traditional sourdough bread culture and previously shown to have antifungal activity against Fusarium species, was tested for inhibition of growth of Fusarium proliferatum M 5991 and M 5689 and F. graminearum R 4053 in a liquid medium setting. This isolate completely inhibited the growth of F. proliferatum M 5689 and M 5991 and F. graminearum R 4053, whereas such growth was not inhibited in the control in a supernatant agar plate assay. When this isolate was tested using 2M medium (MRS-modified Myro media) known for supporting Fusarium growth and trichothecene production, it was found to inhibit fungal growth but promote mycotoxin production at the same time. The antifungal activity was determined to be the result of organic acids and low pH. The mechanism of the mycotoxin production promotion requires further investigation.