Abstract The effect of human umbilical cord extracts on hanging drop cultures of chicken fibroblasts is characterized by an intense cell migration. The stimulating factor has been identified as being the hyaluronic acid. Even after depolymerization by hyaluronidase the stimulating action is retained. This would indicate that only the elementary molecule of hyaluronic acid is involved. No nutritional effect could be demonstrated on long-term cultures and very likely it is rather a spreading property than a growth promoting action which is observed.