An Agrobacterium tumefaciens -mediated transformation (ATMT) system was successfully developed for Colletotrichum truncatum, the causal agent of chili anthracnose. A. tumefaciens carrying a hygromycin phosphotransferase gene (hph) and a green fluorescent protein (gfp) gene was used to transform the conidiospores of two C. truncatum pathotypes F8-3B and BRIP26974. Optimum transformation efficiency was obtained when equal volumes of A. tumefaciens strain AGL1 carrying either pJF1 or pPK2 binary vector was used to transform C. truncatum conidiospores at 10(6) /ml and co-cultivated at 24 °C for three days. Southern blot analysis indicated that 87.5% of the transformants contained randomly inserted, single copies of the T-DNA. Infection and colonisation of chili fruit at the mature red stage with F8-3B-GFP and BRIP26974-GFP confirmed the maintenance of virulence within these transformed pathotypes. In situ studies of infection and colonisation of the susceptible genotype fruit using fluorescent microscopy and transformed isolates of C. truncatum expressing GFP revealed that the pathogen was able to colonise healthy fruit tissue intercellularly in an endophytic manner without producing secondary biotrophic infection structures. The developed transformation system will be used to study the function of pathogenicity genes in C. truncatum using both forward and reverse genetics approaches.