Diaphragm muscle strength was measured as maximal transdiaphragmatic pressure during airway occlusion in ten near-miss sudden infant death syndrome infants aged 4.1 +/- 0.6 (SE) months post-term, range 2 to 7 months, and ten control infants aged 4.5 +/- 0.8 months post-term, range 0.8 to 8 months. In the near-miss sudden infant death syndrome group, the mean maximal transdiaphragmatic pressure was 106 +/- 6 cm H2O, range 78 to 132 cm H2O, compared with a mean maximal transdiaphragmatic pressure 86 +/- 4 cm H2O, range 69 to 106 cm H2O, in the control group. Diaphragm strength is normal or increased in near-miss sudden infant death syndrome infants.