Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that rapidly involves the respiratory system, leading to persistent respiratory insufficiency. Neuromuscular respiratory weakness is also responsible for sleep disordered breathing (SDB), which occurs at an early stage of ALS. Maximal sniff nasal-inspiratory pressure (SNIP) is a sensitive test to early disclose respiratory muscle decline. The aim of this study was to evaluate the role of the SNIP test, compared to FVC, as a marker of SDB in ALS. We studied 31 (18 males) patients with ALS, who were divided into two groups according to the SNIP test value. Ten patients who showed a SNIP value higher than 60 cmH(2)O were considered as group 1. Twenty-one patients exhibited a SNIP lower than 60 cmH(2)O and were included in group 2. Both groups of patients were also investigated with nocturnal sleep study. A linear correlation between lower SNIP value and reduced nocturnal SaO(2) in patients with a SNIP value less than 60 cmH(2)O (n = 21; r = 0.449; p = 0.04) was found. A negative correlation between SNIP and time spent in SaO(2) below 90% (TST90) (n = 21; r = -0.584; p = 0.0054), and between SNIP and oxyhaemoglobin desaturation index (ODI, events/hour) (n = 21; r = -0.458; p = 0.0368) was also established in all the patients of group 2, while, in this group, FVC did not correlate with any nocturnal parameter observed. A positive correlation between SNIP and PaO(2) at baseline of the entire population of patients (n = 31; r = 0.614; p < 0.001) was also seen. In conclusion, the results of this preliminary study show that SNIP < 60 cmH(2)O might be considered an early predictor of SDB in ALS.