Eighty-eight glaucoma patients and 252 normal subjects underwent C-30-2 testing on the Humphrey Field Analyzer. The effect of fixation losses, high false-positive and false-negative response rates on visual field test results was assessed using the mirror image method of detecting asymmetry across the horizontal meridian, and the Humphrey STATPAC pattern standard deviation (PSD) and mean deviation (MD). Glaucoma patients with poor fixation (greater than or equal to 20%) had less depressed fields and fewer localized defects than those with good fixation. Fixation loss did not affect measures of localized defects or generalized depression among normal subjects. High false-positive rates (greater than or equal to 10%) were associated with less-depressed visual fields among glaucoma patients and normal subjects. Visual fields were depressed by an average of 9 dB for glaucoma patients and 7 dB for normal subjects with high false-negative rates (greater than or equal to 33%), when compared with those with low false-negative rates. Apparent localized defects were observed among normal subjects with high false-negative rates. Most of these defects were located in the superior nasal and adjacent arcuate area.