The effects of methotrexate and melphalan in sheep.

1 Sheep were injected with either methotrexate or melphalan in an attempt to lower the numbers of neutrophil granulocytes in peripheral blood. 2 Methotrexate, 5.0 mg/kg intravenously, on three consecutive days, produced no noticeable clinical or haematological changes. 3 A single dose of melphalan, 1.0 mg/kg intravenously, depleted lymphocytes and granulocytes, but the numbers of the latter then rose to values exceeding the levels before melphalan treatment. Doubling the dose of melphalan proved fatal. 4 The failure of methotrexate to produce changes can be explained in terms of ruminant metabolism.