X-ray investigations have shown a complete miscibility in the systems TaS2/MoS2 and TaSe2/ MoSe2. In these systems mixed crystals could be obtained by chemical vapour transport with iodine as transport agent in the temperature gradient 1000→800 °C. By contrast, no mixed crystals are formed in the systems TiS2/MoS2 and TiSe2/MoSe2. The transport behaviour in these systems is reported.