SummaryMastitis commonly occurs in the dairy cow and results in an influx of granulocytes into the mammary gland. Presently, colony stimulating factors have been isolated. One factor, granulocyte colony stimulating factor (GCSF), has been identified and reproduced using recombinant DNA technologies. In an experiment, lactating bovine were given a bacterially‐synthesized human recombinant granulocytic colony stimulating factor (Hr‐GCSF) at a specified dose rate to monitor and characterize their hematological responses. Doses of Hr‐GCSF were administered subcutaneously and blood samples collected from the tail vein into vacutainer tubes. Results of the study indicated a toleration by the bovine for the Hr‐GCSF for the tested period, and that the Hr‐GCSF can stimulate a sustained elevation of circulating ne