In order to expand the collection of promoters studied in Trichoderma reesei Rut-C30, a functional study of the ToxA promoter was carried out by analysis of GFP expression in T. reesei Rut-C30. For this purpose, the binary pCBCT expression vectorwas employed to transformT. reesei Rut- C30. The transformants obtained were evaluated bymeans of fluorescence microscopy, fluorometry, dot blot andWestern blot analysis. The lowlevels of cytoplasmic GFP protein in fungal hyphae suggest that ToxA promoter works as a weak constitutive promoter which can drive successfully the expression of heterologous proteins in T. reesei Rut-C30.