An approximate theory for calculating the line tension in a solid-liquid-fluid system is presented and demonstrated for a solid-liquid-vapor system. The line tension is shown to depend on the contact angle. Consequently, the classical equation for the intrinsic contact angle, in terms of the line tension, is modified. The magnitude of the line tension is shown to be less than 5 x 10(-9) N, and its sign is shown to be positive for acute contact angles and negative for obtuse contact angles. The deviation from the Young contact angle is shown to be negligible for drops of macroscopic size on an ideal solid surface.