Cotton and cotton/polyester fabrics were treated with a proposed antimicrobial formulation based on zinc oxide (ZnO), Impron MTP (binder), and Setamol WS (dispersing agent) under the effect of gamma irradiation. The effect of this treatment on the growth of certain bacteria (Bacillus subtilis) and fungi (Aspergillus niger) was studied. In general, it has been confirmed that ZnO ratio is an inhibitory factor on the growth of both microbes. As a result of treatment of cotton fabrics, as an example, the B. subtilis counts were decreased by 4 log cycles whereas the A. niger count was decreased by 2 log cycles. This finding was illustrated by observing the surface microstructure of the fabrics after they had been buried in a moist soil for two weeks. The deterioration in the weaving structure of the nontreated was so strong that it could not distinguish the strings forming the fabric. On the basis of microbial detection, it was found that the treatment with ZnO formulation causes a net reduction in the bacterial cells amounts to 78 and 62% in the case of treated cotton and cotton/polyester fabrics while the net reduction in the fungi was calculated to be 80.7 and 32%, respectively. However, it was found that the treatment with ZnO formulation caused a reduction in the thermal stability of the fabrics as indicated by thermogravimetric analysis. (C) 2003 Wiley Periodicals, Inc.