A Spanish family is described with two abnormal genes: 1) hemoglobin C in heterozygosis with normal hemoglobin, introduced by the subject's mother, and 2) heterozygotic beta‐thalassemia for which the father is a carrier. In the subject and his sister, both abnormal genes coincide with the presence of hemoglobin C and hemoglobin F, simulating homozygosis for hemoglobin C. The clinical condition shows medium intensity chronic hemolysis. In the subject's brother, mother and grandmother, simple heterozygosis of hemoglobins A‐C is seen, with no apparent clinical manifestations. The father shows subjaundice with some acute hemolytic episodes.