Visual evoked potentials (VEPs) were obtained by monocular stimulation using a checkerboard pattern-reversal and pattern-onset technique. In 11 normal subjects, pattern-onset VEPs were generally larger, better defined, and less ambiguous than those elicited by pattern-reversal, because of the biphasic waveform characteristically obtained with pattern-onset stimulation. In 68 of 105 patients with possible multiple sclerosis, VEPs were normal in latency by both methods, and in nine adequate comparison was not possible. The incidence of normal VEPs to pattern-reversal was similar to that found in several other studies of patients with possible multiple sclerosis. Among the remaining 28 patients in whom VEP abnormalities were found, an increased latency was detected in 75% with the pattern-reversal technique, and in 96% by pattern-onset. In these patients, VEP abnormalities were obtained by monocular stimulation of each of 46 eyes, and among these the pattern-reversal technique yielded abnormalities in 59% and the pattern-onset method in 98%. These results indicate that VEPs elicited by pattern-onset are useful in investigating patients with suspected multiple sclerosis, and the diagnostic yield may be greater than with conventional pattern-reversal techniques.