Organophosphorus (OP) insecticides are widely used as pesticides and produce neuromuscular compromise after acute exposure, paralyzing the rib cage muscles and other muscles. The aim of this study was to evaluate respiratory muscle activity during a weaning test (WT) using eletromyographic signals from a group of six OP poisoned patients (29.5 ± 13.2 years, 68.0 ± 13.9 kg, 162.8 ± 10.6 cm height). High levels of spectral energy at low frequencies in the diaphragm muscle and weak synchronization with the sternocleidomastoid, which is an accessory respiratory muscle, correlated with the success of a weaning test.