Hemostatic disorder in castration wounds or subcutaneous mass hemorrhage occurred in growing pigs weighing 20 to 35 kg on a farm from January to June, 1983. Fifty of 360 pigs displayed clinical signs and 25 pigs died. Twenty-one of 114 pigs (from 5 of 14 groups) revealed abnormal PT on screening tests. These pigs also showed prolonged APTT and decrease in the levels of factors II, VII, IX and X. They were divided into 4 groups for vitamin K administration tests. Vitamin K-1 and K-2 were injected intramuscularly into 8 pigs (K-1 group) and 6 pigs (K-2 group) in a single dose of 3 mg per kg of body weight, respectively. Vitamin K-3 was added to feed at a rate of 25 ppm and given to 3 pigs (K-3 group) for 4 consecutive days. Four pigs (control group) were not treated. Vitamin K-1 and K-2 revealed similar effects on recovery from blood coagulation defects. Thus, in K-1 and K-2 group, PT was improved at 3 hr post-injection, and APTT at 14 or 21 hr. Factors VII, IX and X were elevated to normal levels at 3 or 14 hr post-injection, and factor II at 14 or 21 hr. No pigs in K-1 group demonstrated abnormal PT and APTT on the 5th, 10th and 30th day post-injection. In K-3 group, PT and APTT improved to normal time at 21 hr after the beginning of administration, and no pigs demonstrated abnormal PT and APTT on the 5th or 30th day. In control pigs, there was no recovery from blood coagulation defects for 21 hrs. From these results, the hemorrhagic disease in this study was confirmed to result from vitamin K deficiency. The cause of vitamin K deficiency was considered to be related antibacterial drugs and ingredients of feed.