A method is described for the measurement of the rotational viscosity gamma(1) in nematic liquid crystal cell assemblies. Theoretical formulas to determine gamma(1) from transient current are developed by considering both director rotation and conduction of impurity ions. The pretilt angle and the product of the drift mobility and density of the ions are also obtained with the method. Experimental results for 4-pentyl-4’-cyano biphenyl cells with or without polyimide alignment layers are reported.