This study compares the neuromuscular blocking effect of succinylcholine (0.8 mg • kg−1) and atracurium (0.6 mg • kg−1) on the diaphragm (D) and the adductor pollicis (AP) in 20 patients anesthetized with nitrous oxide, oxygen, and fentanyl. The diaphragm was monitored by measuring transdiaphragmatic pressure following bilateral phrenic nerve stimulation. After succinylcholine, the time from injection of succinylcholine to maximum depression of the single twitch response (onset time) was of 50 ± 11 s (±SD) for D compared to 80 ± 24 s for AP (P < 0.001). After succinylcholine, recovery from paralysis was earlier for D than AP. Single twitch height (TH) returned to 25% of its control value (T25) after 5 ± 2 min for D compared to 7 ± 3 min for AP (P < 0.001). Complete recovery of TH (T100) was achieved after 9 ± 4 min for D and 11 ± 5 min for AP (P < 0.01). Recovery index (T25–75) was of 2 ± 1 min for both muscles. After atracurium, the onset time for D was of 137 ± 31 s compared to 181 ± 45 s for AP (P < 0.001). The T25 was achieved after 38 ± 7 min for D compared to 63 ± 13 min for AP (P < 0.001). The TH of D returned to T100 after 60 ± 12 min compared to 87 ± 17 min for AP (P < 0.01). The train-of-four ratio returned to 1 after 64 ± 15 min for D compared to 99 ± 21 min for AP (P < 0.001). After an intubating dose of succinylcholine (0.8 mg • kg−1) or atracurium (0.6 mg • kg−1), D was always completely paralyzed, when the TH of AP was abolished and the TH of D had completely recovered when the TH of the AP had returned to 100%.