Patients suffering from neuromuscular diseases and thoracic deformities may develop global respiratory failure during their illness. We wanted to judge clinical parameters and information from the patients' medical history to reliably, quickly and noninvasively diagnose a ventilatory failure. Therefore we evaluated 105 situations with and without mechanical ventilation from 29 patients with indication for noninvasive nocturnal mask ventilation. 6 clinical parameters (e.g. heart rate, oxygen saturation, relative vital capacity), 2 test results (pH and partial pressure of carbon dioxide (pCO2)) and 6 parameters from the patients' medical history (e.g. nycturia, frontal headache in the morning, breathlessness) were investigated. After statistical evaluation we could show a relation between heart rate and pCO2 (Spearman's correlation: r = 0.331, p = 0.001, n = 105; one-tailed significance: r = 0.335, p = 0.038, n = 29). Significant differences between the groups of nycturia incidence indicate a tight relation between the incidence of nycturia and the height of hypercapnia levels (ANOVA--analysis of variance: p = 0.001). Using logistic regression we could show that information regarding medical history, especially nycturia, frontal headache and indrawings, gives important indications for global respiratory failure (sensitivity 97.62-100%, specificity 57.14-76.19%). Pathogenesis needs to be elaborated further.