Abstract: In the preparation of high molecular weight polyamides, vaporization of the organic diamine employed results in its loss. The effect of the loss can be reduced by collecting the vapor given off during the evaporation and/or polymerization steps, condensing it, passing the condensate through a selected ion-exchange resin, and obtaining the diamine by contacting the resin with either a strong inorganic acid or an aqueous solution of an organic dicarboxylic acid used in making high molecular weight polyamides depending upon the resin employed. When the diacid is used, the salt so obtained can be used in preparing high molecular weight polyamides.