A rapid and simple simultaneous micropurification procedure of tyrosine hydroxylase (TH) and dihydropteridine reductase (DPR) was developed from soluble supernatants of 1 to 2 g of rat adrenal gland or caudate nucleus. All purification procedures for the two enzymes were complete within 3 days. The recovery of TH and DPR was reproducible and approximately 20 and 40%, respectively. Purification procedure for TH involved chromatographies with DEAE-Sephacel, Bio-Gel A-1.5 m, and heparin-Sepharose. As judged by gel filtration and sodium dodecyl sulfate-gel electrophoresis, the enzyme purified from each tissue appeared to be homogeneous and was composed of an identical subunit, each possessing a Mr of 60,000. With DEAE-Sephacel column chromatography, TH was separated completely from DPR. DPR was purified by subsequent chromatographies with Sephadex G-50 and blue Sepharose to a purity of 50%. DPR in adrenals and brain was found to be a NADH-dependent type. This micropurification procedure is applicable to assessing the molecular properties of TH modified physiologically or pharmacologically in vivo, and to getting a small amount of the pure enzyme as antigen for producing its antibody.