In dim illumination and empty visual fields, accommodation in most observers is for an intermediate distance referred to as the dark focus or resting focus of accommodation. Dynamic properties of the resting focus were examined in the present study with a high-speed IR optometer. All subjects displayed fluctuations of accommodation in darkness that were primarily characterized by frequency components below 0.5 Hz. These fluctuations were substantially attenuated during cycloplegia or viewing a bright, high-contrast target. Both the mean resting-focus position and the magnitude of fluctuations varied from 1 subject to another and from day to day. A weak association was found between the mean and standard deviation of accommodation responses in the dark. The accommodation mechanism in most observers apparently is somewhat unstable under degraded viewing conditions. The mean resting-focus value for a large sample of subjects was found to be lower for IR optometer measurements than for previous investigations employing a laser optometer.