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The ventilatory response to hypoxia and to hypercarbia was assessed in 36 near-miss sudden infant death syndrome (N.M SIDS) and 23 control infants. Base-line measurements during non-REM sleep documented no significant difference in respiratory frequency, alveolar CO2 and O2 partial pressure (PAco2 and PAo2) or tidal volume between the N-M SIDS and control infants. In the N.M SIDS group, mean inspiratory flow and minute ventilation (VI) were significantly lower than in the control group (p less than 0.001 and p less than 0.01, respectively), and the slope of the ventilatory response to hypercarbia ((delta VI/Torr Paco2) was only 21 +/- 1.9 (SE) ml.kg-1 min-1 Torr PAco2 compared with 62 +/- 3.5 in controls (p less than 0.001). For both groups, the increase in ventilation with hypoxia appeared linear within the PAo2 range assessed (65-115 Torr) and was therefore expressed as the slope of the delta VI/PAo2 plot (ml.kg-1 min-1 per Torr PAo2). The slope of the hypoxic ventilatory response was significantly less in the N-M SIDS than in the control group, -8.3 +/- 1.0 VS. -19.9 +/- 1.5, respectively (p less than 0.001). In summary, in comparison to control infants, N-M SIDS infants as a group have a significantly smaller increase in VI in response to hypoxia as well as to hypercarbia.