The relation between the pattern of fumonisin production and the mating population and mating type of Fusarium isolates from maize in Argentina at different maturity stages has been evaluated. Fifty-one isolates of Fusarium species belonging to the Liseola section were identified to mating population and tested for their ability to produce fumonisins (FB1, FB2 and FB3). Only mating populations associated with maize, A (Fusarium moniliforme, 23 isolates), D (F. proliferatum, 24 isolates) and E (F. subglutinans, 4 isolates) were found. All but two isolates of populations A and D produced, when grown on maize substrate, high levels of fumonisins ranging from 0·01 to 3·99 mg g−1 (mean 2·00 mg g−1 and 1·69 mg g−1, respectively), whereas isolates of population E yielded less than 0·02 mg g−1 (mean 0·01 mg g−1). Five isolates of F. proliferatum, all belonging to mating type D−, produced more FB2, than FB1, which is consistent with finding a relatively large amount of FB2 (0·01 mg g−1; FB2/FB1=2·27) in one of the maize samples from which these isolates were obtained. Amounts of FB3 were similar to FB2 in cultures of mating population A (mean FB3/FB2=0·89), but much lower than FB2 in cultures of mating population D (mean FB3/FB2=0·21).