The cholesteric pitch P of semiflexible helical polymer solutions was formulated using a threaded equivalent freely jointed chain model. The theory was favorably compared with experimental results of P for cholesteric solutions of the three helical polymers schizophyllan (a triple-helical polysaccharide), poly(gamma-benzyl L-glutamate), and poly((R)-2,6-dimethylheptyl isocyanate), and two chiral interaction parameters characterizing the chiral hard-core repulsion and the soft dispersion force were determined from this comparison. However, the same theory failed to describe the polymer concentration dependence of P for cholesteric solutions of (acetoxypropyl)cellulose in a very concentrated region.