We propose a method to determine the isoscalar (K) over barN scattering length on the lattice. Our method represents the generalization of Luscher's approach in the presence of inelastic channels (complex scattering length). In addition, the proposed approach allows one to find the position of the S-matrix pole corresponding the Lambda(1405) resonance. (C) 2009 Elsevier B.V. All rights reserved.