Usefulness of subjective sleep quality assessment by a questionnaire (OSA-MA sleep inventory) was examined in ten track drivers (age, 42 +/- 12 y, range, 23-62 y) in reference to the objective measure of sleep apnea by cyclic variation of heart rate (CVHR) in electrocardiogram (ECG) during sleep. Total CVHR suggesting moderate-to-severe sleep apnea (average over total time in bed > 15 cycles/h) was observed only in one subject and the transient occurrence of frequent CVHR (= 50 cycle/h) was detected in the same subject and two other subjects. The questionnaire provided the standardized scores of five features of subjective sleep quality, including less sleepiness on rising, good initiation and maintenance of sleep, less frequency of dreaming, refreshing feeling, and subjective sleep length as factors 1-5, respectively. The subject with high average CVHR showed factor scores < -1 SD for factors 1, 2, and 3 and reported subjective sleepiness during driving. In the two subjects with transient frequent CVHR, one showed factor score < -1 SD for factors 3 and 5, while the other did not show score < -1 SD for any of the factors. Although this is preliminary study in a small sample size, it suggests the possible associations between the subjective assessment of sleep quality and the objective measure of CVHR.