This report, which is of a preliminary nature, deals with the species of Culicidae met with in Macedonia by the British Malaria Commission during the latter half, of 1917. The collections of the Commission have been augmented by material forwarded from time to time to the Malaria Enquiry Laboratory, Salonika, by various Medical Officers and others in the field. While engaged in working out these and other blood-sucking Arthropods, I had the privilege of examining, through the kindness of Dr. Joyeux, of the Mission Antipaludique, samples of species taken within the areas under French control. As our reports are to appear almost simultaneously, and as my colleague has devoted special attention to the larval morphology of these insects, I have confined myself here mainly to the adults, and field notes. I desire to thank heartily the following officers for material and notes supplied—Majors Bissett and Armour; Captains Boyd, Candler, Peacock and Carnwath. I have also been indebted in many ways to the kindness of Lt.-Col. C. M. Wenyon, O.C. the Malaria Enquiry Laboratory. For the work of identification the Trustees of the British Museum (Nat. Hist.) have afforded every facility, and in this connection my best thanks are due to Mr. Lang of the Museum Staff. Again, as on many another occasion, it is a pleasure to acknowledge the assistance ungrudgingly rendered by Dr. G. A. K. Marshall, Director, Imperial Bureau of Entomology.