Neither with sunlight nor with intense long ultraviolet LUV radiation was it possible to produce phototoxic reactions with orally administered doses of methoxsalen (8-methoxypsoralen [8-MOP]) customarily used to treat vitiligo and to promote tanning. The optimal time of exposure was two hours after ingestion. A single dose was as effective as the same dose given daily. Hot quartz ultraviolet lamps should not be used. A suitable source of LUV light is a bank of four black lights placed close to the skin. With 45 minutes of exposure at 6 inches, 40 mg of methoxsalen will consistently produce a phototoxic response. The dose may be raised to 60 mg as required.