First trimester procedures have been associated with perinatal lung function abnormalities that may suggest subsequent respiratory problems. Our aim was, therefore, to assess the impact of first trimester invasive procedures [early amniocentesis (EA) and chorion villus sampling (CVS)] on respiratory morbidity in very young children. A questionnaire was issued to parents of 439 EA and 453 CVS (subjects), and 435 controls (their mothers had undergone no invasive procedures) when their children were one year old. Data were also obtained from diary cards issued to a subset of 278 of the EA, 262 of the CVS, and 264 of the control infants followed prospectively. Functional residual capacity (FRC) was measured at a median age of 5 months (range: 0.25-24) in 159 children whose mothers had undergone EA, 168 following CVS and in 165 controls. Analysis of the one-year questionnaire demonstrated an excess of symptomatic infants in the EA group (31%) compared to the CVS (22%; P < 0.01) and control groups (17%; P < 0.01). Findings from the prospective follow-up study confirmed those results and also demonstrated an increase in chest-related hospital admissions in the EA group (3%) compared to the controls (0.4%; P < 0.05). Logistic regression analysis revealed that positive symptom status related significantly to EA and CVS interventions (P < 0.0001), bottle feeding (P < 0.001), parental smoking (P < 0.01), a family history of atopy (P < 0.01), and immaturity (P < 0.01). In the control group, FRC correlated best with weight (r = 0.92). The mean FRC of the EA and CVS groups was higher than that of the controls (P < 0.01). A higher proportion of children had an FRC two standard deviations above the controls' mean in the EA group (n = 14) compared to the CVS group (n = 3; P < 0.01). The symptomatic infants tended to have higher FRCs than the asymptomatic children. We conclude that first trimester procedures are associated with increased respiratory morbidity in very young children.