Si Wu Tang is the representative formula for tonifying the blood. The original formula of Si Wu Tang is composed of the following individual herbs: 12g Shu Di Huang (Rehmannia), 9g Dang Gui (Angelica), 9g Bai Shao (Paeonia), and 6g Chuan Xiong (Ligusticum). The Chinese therapeutic actions of this formula are to nourish the blood and regulate blood circulation. All of the herbs in this formula enter the blood level. Blood deficiency usually manifests in such signs as pale mucous membranes, a pale, dry tongue with a white tongue coating, and a thready, weak pulse. Other common clinical signs include pruritis, dryness, dandruff, a thin, brittle hair coat, cracked hooves and paw pads; these signs are the result of the inability of the blood to nourish the skin and hair coat. Clinically, Si Wu Tang can be used to treat anemia, postpartum anemia, threatened abortion, infertility, insomnia, chronic nephritis, chronic itching and dermatitis, atopic dermatitis and urticaria. Si Wu Tang should be used with caution in animals with deficiency of the Spleen and Stomach, because the rich, stagnating nature of Shu Di Huang could affect digestion. Spleen tonics are often used concurrently when administering this formula; it should be avoided in animals with dampness or Qi deficiency without modification as it can cause vomiting. The pharmacological effects of Si Wu Tang include hematopoietic, radioprotective, anti-pruritic, anti-inflammatory and anti-neoplastic.