The vesicular arbuscular mycorrhizal (VAM) fungi are root symbionts associated with many vesicular plant species. The contribution of VAM fungi on uptake of herbicides by plant root systems and degradation of herbicides in the rhizosphere and the consequent effects on herbicide tolerance by crop plants were investigated. The results of the different studies conducted on herbicide uptake have demonstrated that colonization of corn and soybean by the VAM fungus, Glomus epigaeus enhanced the efficiency of root uptake of atrazine and trifluralin. The hyphae of G. epigaeus were able to absorb 14C-atrazine from soil and translocate to corn plants. Experiments conducted on the effect of mycorrhizal and nonmycorrhizal rhizosphere on atrazine degradation in soil showed that degradation of atrazine in soil was not affected by corn and G. epigaeus. Rhizosphere and presence of G. epigaeus enhanced bound residue formation in soil. Experiments were conducted in greenhouse conditions using low and high P soil that simulated exposure of soybean and corn to atrazine and trifluralin, respectively due to carry-over. Colonization by VAM fungi significantly enhanced P uptake and plant growth at lower concentrations of herbicides. There was no effect of VAM fungi on plant growth in high P soil. In low P soil the positive effects of VAM fungi on plant growth due to enhanced P uptake were more important than any negative effects due to increased herbicide uptake.