An improved method for the measurement of catecholamines in brain parts has been developed, based on reverse-phase ion-pair chromatography. The new method offers the advantages of high efficiency microparticulate liquid chromatography packings and the flexibility of ion-pair chromatography. By this approach norepinephrine and dopamine (DA) have been measured in the hypothalamus and corpus striatum of the rat brain during various stages of development (15, 21, 30 days). Data are reported on the basis of the whole part and per weight of tissue. For the adult animals, the following concentrations (ng/g wet tissue) were observed for the hypothalamus: NE = 2261 ± 274, DA = 440 ± 103, and for the corpus striatum: DA = 11,888 ± 1840. The overall precision of the method was ±5.6% relative s.d. The absolute recovery was 60 ± 5% relative s.d. and was constant over the range of 1 ng to 1 μg of dopamine or norepinephrine per tissue sample. The relative retention behavior of 18 neurologically important catechol derivatives is reported for reverse-phase chromatography with octyl sulfate as the stationary phase modifier.