The use of ultraviolet radiation as the source of illumination in perimetry is comparatively new. As yet only a preliminary report has been published concerning its general and specific applications.1 Perimetry with ultraviolet (Blacklight) radiation has introduced luminescent test objects in color whose spectral band is so narrow that for practical purposes they are monochromatic stimuli with a saturation and purity of color surpassing any of the previously used papers. Because the luminescent phosphor of the blue test object selectively absorbs only the wave length from 450μ to 475μ, it emits blue light within a very narrow band. It is possible to narrow this wave-length band still further by the use of filters. This investigation will report clinical observations when monochromatic blue stimuli are used in the examination of the visual field. Normal visual fields for the blue stimuli were first established, after which a variety of visual field