A simple modification of the Pitzer relation to calculate second virial coefficients of polar compounds is proposed. The proposed modification is based on the use of a new parameter, beta, which embodies both the contributions of acentricity and polarity to second virial coefficient values. The analytical form of the Pitzer relation is preserved and its performances are improved. Rules are given to calculate beta for several classes of compounds which require only the knowledge of a few well known properties of pure compounds. A comparison between the new method 1 and the Pitzer-Tsonopoulos relation is made on the basis of the experimental B-i data of nearly 50 compounds.