A combined method was developed for characterization and differentiation of catecholamines in neuron populations containing more than one catecholamine, e.g. dopamine and norepinephrine. Its application to small intensely fluorescent (SIF-) cell clusters in sympathetic ganglia allows the successive demonstration of glyoxylic acid-induced catecholamine fluorescence and dopamine-beta-hydroxylase by indirect immunofluorescence within the same tissue section. Applying this technique to an example, two types of SIF-cells were demonstrated in the guinea pig superior cervical ganglion.