Selective photothermolysis (SP) is a novel technique by which brief, unfocused laser pulses are selectively absorbed by, and cause selective thermal damage to, endogenously pigmented structures. The present experiments demonstrate the feasibility of using an exogenous non-fluorescent chromophore (procion blue) to effect cellular damage by SP. Dorsal root ganglia neurons in vitro were selectively labeled with procion blue and subsequently damaged by unfocused laser illumination. Progressive cellular damage was assessed by propidium iodide (PI), a fluorescent dye that leaks through damaged membranes and binds to nucleic acids. Graded scores of intracellular PI fluorescence demonstrated a highly significant difference in amount of damage between groups of experimental and control cells. Selective photothermolysis is discussed as an experimental tool for neurobiologists in particular and for general use within the biomedical field.