An analysis of waveform velocities was performed on 16 individuals with congenital nystagmus. The fast phases were shown to be saccadic in nature and their main sequence peak velocity was significantly slower than that of the normal control group (P less than 0.01). Peak slow phase velocities were found to reach values as high as 180 deg/sec; a relationship between the peak slow phase velocity and the amplitude of the slow phase was demonstrated. The range of the velocities that comprise the slow phase was generally in excess of 100 deg/sec. The correlation between the period of time spent at low retinal slip velocities (less than or equal to 10 deg/sec) and visual acuity was found to be significant (P less than 0.05). Implications of high slow phase velocities are discussed with reference to future experimental design.