(omega-1)-Fluoroalk-(omega-1)-enoic acids of chain lengths varying between C-5 and C-15 have been prepared by consecutive bromofluorination and dehydrobromination of either alk-(omega-1)-enoic acids or alk-(omega-1)-enyl acetates, in the latter case followed by oxidation. The halogen was found to increase the antimycotic properties of the unsaturated fatty acids, 10-fluoroundec-10-enoic acid exhibiting a particularly strong fungicidal activity.