D-D mixture is a preplant soil fumigant. It contains dichloropropanes and dichloropropenes, epichlorohydrin and is known as a primary irritant. Three cases of untoward reaction to D-D are reported. By patch testing, the existence of a contact allergic sensitivity to D-D could be proved in one patient. The other two cases reacted negatively; they were probably of a primary irritant origin. Patch tests with compounds related to D-D suggest that the cause of contact allergy must be sought in the propene(s) fraction of D-D. In future cases of untoward reactions to D-D, patch testing appears to be necessary in order to differentiate between a contact allergic and a primary irritant reaction.