This study tests the hypotheses that a recruitment maneuver per se yields and/or intensifies lung mechanical stress. Recruitment maneuver was applied to a model of paraquat-induced acute lung injury (ALI) and to healthy rats with (ATEL) or without (CTRL) previous atelectasis. Recruitment was done by using 40 cmH₂O CPAP for 40 s. Rats were, then, ventilated for 1 h at ZEEP or PEEP (5 cmH₂O). Atelectasis was generated by inflating a sphygmomanometer around the thorax. Additional groups did not undergo recruitment, but were ventilated for 1 h under ZEEP. Lung resistive and viscoelastic (P2) pressures, and static elastance (Est) were computed before and immediately after recruitment, and at the end of 1-h ventilation. Lungs were prepared for histology. Type III procollagen (PCIII) mRNA expression in lung tissue was analyzed by RT-PCR. Lung mechanics improved after recruitment in the CTRL and ALI groups. One-hour ventilation at ZEEP increased alveolar collapse, Est and P2. Alveolar collapse was similar in ATEL and ALI, and recruitment opened the alveoli in both groups. ALI showed higher PCIII expression than ATEL or CTRL groups. One-hour ventilation at ZEEP did not increase PCIII expression, but augmented it significantly in the three groups when applied after recruitment. However, PEEP ventilation after recruitment avoided any increment in PCIII expression in all groups. In conclusion, recruitment followed by ZEEP was more deleterious in ALI than in mechanical atelectasis, although ZEEP alone did not elevate PCIII expression. Ventilation with 5 cmH₂O PEEP prevented derecruitment and aborted the increase in type III procollagen expression.