Uptake of 3H-dopamine in the pedal ganglion of Quadrula pustulosa was localized using combined fluorescence and optical light microscopy, in addition to electron microscope autoradiography. Light microscope autoradiograms of the same sections previously prepared for fluorescence microscopy indicated most radioactivity occurred over green, long-lasting fluorescent fiber tracts and nerve cell bodies. Ultrastructural autoradiographic results showed the majority of the radioactivity was localized over synaptic vesicles. Nerve fibers containing neurotubules, and also a limited number of nerve cell bodies were labelled with 3H-dopamine. These results suggest uptake of dopamine to be specific for dopaminergic structures.