Colony stimulating activity in normal human serum tested against human bone marrow

Two hundred and thirty normal human sera have been tested for colony stimulating factor (CSF) under carefully controlled conditions using human bone marrow and the semi-solid agar-gel technique. It has been shown that CSF can be detected in most sera when incorporated into underlayers to remove potential inhibitors. The effect of storage temperature on serum CSF has been determined. Storage at 4 degrees, --15 degrees, and --66 degrees for up to 80 days resulted in only a mild decrease in CSF levels. After 240 days of storage, CSF values fell to 50% of that found before storage. Repeated freeze-thawing of serum has not been shown to decrease CSF levels when done in Pyrex glassware. These studies will serve as a baseline for those wishing to study human serum CSA in hematopoietic disorders.