Capsular and somatic antigens were determined in 100 Kl. oxytoca strains isolated from patients with the respiratory tract inflammations. K antigens were assigned by the capsula swelling test using 77 specific anti-capsular sera. Most frequent were: K14, K2, K55, K8 and K16 antigens. Positive reaction was noted with 64 strains in 2 or more sera. Somatic antigens of Klebsiella oxytoca bacilli were tested by the test tube agglutination reaction. Of 63 strains tested with anti-01 Kl. pneumoniae and Kl. oxytoca sera, all reacted positively in anti-0 Kl. oxytoca serum and 77% strains in anti-01 Kl. pneumoniae serum. Of 29 strains agglutinating in anti-03 sera, 65.5% agglutinated with anti-0 Kl. oxytoca serum and 76% with anti-03 Kl. pneumoniae. The results have revealed that Kl. oxytoca strains investigated have more complicated capsular antigens and different frequency of their occurrence. The most commonly encountered somatic antigen is antigen 01, next in turn is antigen 03, these antigens proved nonidentical with their 01 and 03 counterparts in Kl. pneumoniae strains.