BACKGROUND: Despite few studies, a monitoring of a neuromuscular blockade with a train of four (TOF) is recommended in intensive care unit (ICU). Our objective was to compare the results of ulnar and facial TOF measurements with an overall clinical assessment for neuromuscular blockade in ICU patients treated with recommended doses of atracurium or cisatracurium, including patients with acute respiratory disease syndrome (ARDS). METHODS: We prospectively included in two ICUs 119 patients, 94 with ARDS, who required a neuromuscular blockade for more than 24 h. Three levels of neuromuscular blockade were defined: "over-paralyzed" (TOF = 0), "well-paralyzed" (TOF = 1-2), and "under-paralyzed" (TOF = 3-4). Physicians blinded for TOF counts were asked to classify patients clinically as "over-paralyzed," "well-paralyzed," or "under-paralyzed". Patients were assessed two times daily. RESULTS: For the whole population 996 ulnar and facial TOF measurements and clinical assessments were obtained (846 with cisatracurium and 150 with atracurium). Proportions of patients classified as over-paralyzed, well-paralyzed, and under-paralyzed based on TOF measurements and clinical assessments differed significantly (p < 0.0001). The number of observed agreements between clinical assessments and facial TOF measurements was of 19.08% (κ = 0.06) and of 17.37% with ulnar TOF measurements (κ = 0.04), while it was of 62.75% between ulnar and facial TOF measurements (κ = 0.45). Results were similar for cisatracurium and atracurium. Repeated facial TOF measurements performed on the first 4 days of mechanical ventilation in ARDS patients showed that the proportion of patients TOF = 1-2 was around 8% and did not vary significantly with time (p = 0.9), proportion of patients TOF = 3-4 increased from 24 to 40% (p = 0.01), proportion of patients TOF = 0 decreased from 71 to 53% (p = 0.005) while objectives for protective ventilation were achieved. Proportions of facial and ulnar TOF = 0 were significantly higher among patients with ICU-acquired weakness (ICU-AW) versus those who did not develop ICU-AW (51 vs. 40%, p = 0.03, and 76 vs. 62%, p = 0.006, respectively). CONCLUSIONS: The study provides data on clinical and TOF monitoring of neuromuscular blockade, which are widely divergent in ICU patients receiving recommended doses of benzylisoquinoliniums.