HgCdTe crystals have been grown from CdTe seeds by the travelling heater method (THM). Three different kinds of interfaces between the growing crystal and the seed were found: a sharp planar interface; a non-planar interface which is caused by meltback near the ampoule walls; a diffuse zone, where an interface cannot be discerned. A correlation was found between the initial growth parameters and the interface structure. Microprobe analysis revealed a boundary layer which, in the case of the planar interface, had an unusual shape. This layer had a thickness varying from 400 to 800 microns. It consisted mostly of HgTe, and contained holes as defects.