Electroviscous effects are important in a number of technologies, for example, how of electrolytes through synthetic membranes (which may have capillary pores) and filter cakes, Although the equations governing the effects are well known, previously published solutions have to a large extent involved analytical approximations, This paper presents two significant advances in the calculation of such effects, First, a numerical solution of the nonlinear Poisson-Boltzmann equation for a cylindrical pore is developed, The solution is facilitated by a substitution to reduce the stiffness of the equation, Second, the analysis of electroviscous effects has been extended to symmetric electrolytes in which the mobilities of anions and cations may be individually specified. It is shown that the calculated electroviscous effects are strongly dependent on the mobility of the ion of opposite sign of charge to the capillary wall (counterion) even if the coion is kept the same. Ah of the calculations may be easily performed on a PC.