Snoring (I). Daytime sleepiness in regular heavy snorers. Fifteen men, mean (means) age 44 years, were investigated. Their means body mass index was 21.9 kg/m2, and all of them had a respiratory disturbance index below 5 and had good nocturnal oxygen saturation. The subjects were monitored several nights both with and without the following devices: a tight-fitting facial mask, a pneumotachometer, and an esophageal balloon. They were also monitored with and without nasal continuous positive airway pressure. The Multiple Sleep Latency Test was administered after three of the experimental nights (after the baseline nights and after the second nasal CPAP night). Determination of short EEG arousals during nocturnal sleep, which lasted 2 to 10 s, was performed. The relationship between short EEG arousals, the esophageal pressure nadir, and airflow decrease was investigated. We also determined the relationship between clinical reporting of decrease in daytime alertness and MSLT results, and the relationship between MSLT results and the frequency of EEG arousals. The monitoring indicated that heavy snorers may present significant increase in Pes nadir with abrupt decrease in flow leading to EEG arousals. The frequency at which EEG arousals occur has an impact on MSLT scores. Nasal CPAP improves MSLT scores and eliminates these respiration-related EEG arousals. Some heavy snorers without obstructive sleep apnea syndrome may be at risk of having a decrease in daytime alertness. 