F. B. Hutt, C. G. Rickard and R. A. Field (J. Hered., 39, 3 ; 1948) describe the discovery of a sex-linked hæmophilia in dogs. This shows as a lameness and by swellings in various parts of the body when the puppy is six weeks old. Examination showed that the lameness was due to hæmorrhage at the joints. Of seventeen puppies which have been recognized as hemophilics, not one has been raised to maturity. Several tests for hæmophilia in man Were applied to these dogs and were found to give positive results. The breeding histories of the parents of the puppies were known ; as a result, it was easily seen that the condition was due to a sex-linked recessive gene called h. The importance of the discovery lies in the fact that the comparative physiology of dog and man is well known, and the condition will be of value in research. It is noteworthy that this case in dogs is one of the few sex-linked genes in mammals other than man where seven or eight sex-linked characters are known. The pig has an inherited hæmophilia ; but this is controlled by a recessive gene on an autosome. It is probable that paralytic or lame puppies which were destroyed in the past were in reality sometimes hæmophilic. It would be desirable to discover whether any hæmophilic puppies survive to maturity ; on the different genetic backgrounds of different breeds, the recessive gene may not always have a lethal effect.