The effect of the inoculum potencial for Colletotrichum gossypii was studied based on the amount of damping-off produced on cotton seedlings under greenhouse conditions. The amount of damping off caused by G. gossypii increased as the concentration of conidia increased from 5 to 57.500 conidia per mililiter. When the concentration of conidia of all isolates, was adjusted to 575 conidia per mililiter, the amount of dasmping-off produced, was the same for all isolates, with the exception of one. When the inoculum produced by the different isolates was tested without any adjustement for the concentration, the isolates showed a wide range of pathogenicity. The cotton varieties IAC-RM2, IAC-RM3 and I AC-12-1 were less susceptible to C. gossypii than the varieties IAC-RM2 S.M. and ACALA 61/60. The variety RM4 showed to be intermediate in susceptibility when compared to the two groups.