Plasma levels of methotrexate, dichloromethotrexate, and their 7-hydroxy metabolites can be determined quickly and accurately by direct analysis in a high pressure liquid chromatographic system. This system utilizes a precolumn of CO:Pell ODS resin to protect the analytical mu-Bondapak C18 column. The precolumn also provides a bed for extraction of drugs from the plasma proteins which are trapped in it. Elution with a paired ion solvent provides good recovery of methotrexate from the plasma and excellent separation on the column. The primary advantages of this system are its speed and simplicity combined with its ability to determine the plasma level of parent drug and its metabolite simultaneously.