Visual markers detectable by histochemical staining have been developed for analysing the time course and tissue specificity of maize infections by Fusarium moniliforme. Three F. moniliforme strains, RRC 374, MRC 826 and RRC PAT, were transformed with a plasmid, pHPG, containing the gusA reporter gene which codes for β-glucuronidase (GUS) and the hph gene for hygromycin resistance as the selectable marker. Introduction of plasmid DNA into germinating conidia yielded 1·2×10−7 transformants per conidium; expression of both gusA and hph was however, transient. Stable transformants were obtained using protoplasts as the recipient, but transformation frequency was reduced. Southern blot and PCR analyses confirmed incorporation of pHPG into the genome of all three F. moniliforme strains with gusA properly inserted in MRC 826 and RRC PAT, but apparently disrupted in RRC 374. The growth pattern for transformed F. moniliforme isolates and the parental wild types followed a sigmoid curve on minimal and enriched media. Hygromycin totally inhibited growth for wild type isolates, but not of transformants. Transformed isolates maintained the ability to infect the maize plant. Thus, this study is the first report of F. moniliforme transformed with a visibly detectable reporter gene to use for analysing this endophyte-host interaction of world-wide importance to animal and human health.