Serial confocal images of serotonergic (5HT) cells were collected from fluorescently labelled immunostained larvae of the sea starPatiriella regularis.Compared with results obtained by conventional epifluorescence microscopy of the same specimens, laser scanning confocal microscopy (LSCM) produced superior resolution of the 5HT positive cells at the larval surface and at depth. Three-dimensional (3-D) reconstructions of optical sections were used to view the larvae from different angles to follow the development of the 5HT positive cells, thus avoiding the need to physically move the specimens. Immunoreactive cells were first seen in the apical region of the gastrula. This was followed by the appearance of cells in the mid-region of the gastrula. By the bipinnaria stage 5HT immunoreactive cells were present around the oral hood where they formed lateral ganglia near the mouth. Confocal laser scanning microscopy and 3D computer reconstruction of the larvae represents a methodological improvement for the study of echinoderm neurogenesis because the position of the labelled cells can be determined nondestructively without the need for microtomy and geometric reconstruction.