Sleep disruption in ALS/MND is related to hypoventilation and nocturnal O(2) saturation. Maximal inspiratory pressure (PI(max)) proved sensitive in predicting nocturnal O(2) saturation. However, PI(max) is highly dependent on patient collaboration; on the other hand Mouth Occlusion Pressure (MOP) is a reliable, non-volitional parameter index of central respiratory drive. Since exercise testing (ET) is also part of the assessment of ventilatory regulation the authors aimed to determine whether MOP and ET are sensitive and reliable parameters predictive of nocturnal O(2) saturation and clinical evolution. We conducted a Polysomnographic (PSG) study in two groups of 14 patients, selected according to their MOP level. Patients performed at admission an ET, Respiratory Function tests (RFT) and clinical evaluation with Norris spinal and bulbar scores (SNS and BNS). All patients in Group I (Low MOP) had decreased O(2) saturation during ET (P<0.001). Correlation study showed correlation between ET and MOP (R=0.6); PI(max) slope and PE(max) slope correlated with ET (R=-0.4; -0.6), respectively. ET also correlated with nocturnal O(2) saturation and SNS slope (R=0.8; -0.5), respectively. SNS and BNS slopes correlated with nocturnal O(2) saturation (R=-0.4; -0.7), respectively. The best correlations found were between MOP slope and BNS slope and SNS slope (R=0.8; 0.7), respectively. The high predictive values of MOP and ET at admission to nocturnal O(2) saturation (predicted value=80%) suggested the need of nocturnal pulse oximetry as a standard procedure. MOP and ET should also be used in evaluation protocols of ALS/MND.