In snoring men improved nasal breathing during sleep has been shown to decrease snoring and morning tiredness. The aim was to evaluate whether improved nasal breathing had any effect on growth hormone (GH) secretion, the nocturnal secretion of GH being associated with deep sleep. Forty-two snoring men, mean age 45 years and mean body mass index 26 kg.m-2, slept every night during one month with the Nozovent nostril dilator. Before and at the end of the test period, we analysed serum insulin-like growth factor 1 (IGF-1), thyrotropin (TSH), free thyroxine (free T4), free 3,5,3'-triiodothyronine (free T3), cortisol and testosterone in blood sampled at 08:00 h. Fifteen of the 37 snoring men who completed the study experienced a reduction in snoring and were less tired in the morning during the test period. In this group, the mean IGF-1 concentration was significantly increased (p < 0.05) after one month. There was no significant difference in mean IGF-1 level between the snorers and a population sample. Likewise, TSH, free T4, free T3, cortisol and testosterone concentrations were within normal limits. Snorers with reduced snoring and morning tiredness due to improved nasal breathing showed an increase in morning IGF-1 concentration which can probably be explained by higher nocturnal GH secretion induced by more deep sleep.