Spatial contrast sensitivity was measured over a 6 log unit luminance range in two cats before and after bilateral 4-5 deg radius argon laser lesions were placed in area centralis. The lesions reduced high luminance contrast sensitivity by approximately 0.3-0.4 log units at the low and middle spatial frequencies and by 0.5-1.0 log unit at the highest spatial frequencies. The loss of visual acuity was 0.4 octave in the cat with the smaller lesions and 0.8 octave in the cat whose lesions were larger. At lower luminance, little loss in contrast sensitivity was seen and no change was detectable at scotopic luminance levels. Visual acuity, on the other hand, was decreased at higher scotopic conditions, but unaffected at the lowest luminance levels tested (16 X 10(-6) cd/m2). These data indicate that area centralis plays an important role in detecting both high and low spatial frequencies under high luminance conditions but contributes only to spatial resolution at low luminance levels. This result is consistent with known anatomical and physiological properties of the cat area centralis.