A method is described for determining the torsional stiffness at the cracked stage of reingforced concrete members subjected to pure torsional moments. The method is based upon a truss analogy for torsion. Theoretical expressions are deduiced for the torsional stiffness of beams of arbitary and rectangular cross-sections. The theoretical values are compaerd with experimental results for rectangular beams. The applicability of the theory used is briefly discussed and a procedure is given to correct for its imperfections.