The effect of polymer networks is studied for highly twisted nematic liquid crystals. A numerical relaxation technique was used to minimize the free energy density of a liquid crystal medium. Assuming the networks are distributed uniformly, an polymer network contribution to the system lice energy is added in the form of -1/2K(a)((n) under bar . (N) under bar)(2), where K-a, (n) under bar and (N) under bar are polymer network coefficient, liquid crystal director and polymer network unit vector, respectively. Ignoring the polymer networks elasticity, the liquid crystal director configuration and elastic energy under the influence of an external electric field are calculated numerically. The obtained electro-distortional characteristics are found to depend on the value of K-a and (N) under bar. The results are compared to the electro-optic threshold and hysteresis behaviors of a set of highly twisted nematic calls with different monomer concentrations. The elastic energy of the liquid crystal medium is used to describe its bistability.