A computer simulation method is devised whereby the change in location of a triple point is followed as one of the parameters of the interaction potential is modified. The method, a two-dimensional Clapeyron integration, is illustrated here for the case of a hard-core plus repulsive Yukawa potential of variable range. The latter is a crude model for charge-stabilized colloids. It is shown that the body-centered-cubic (bcc) phase becomes metastable when the range of the Yukawa term is smaller than, approximately, one-sixth of the hard-core diameter. (C) 2000 American Institute of Physics. [S0021-9606(00)51310-5].