Nasal nitric oxide levels are low in patients with primary ciliary dyskinesia, but it is not known whether this defect is already present in the first months of life. The current authors measured nasal nitric oxide in two infants with situs inversus and primary ciliary dyskinesia, diagnosed by electron microscopy at 4 and 6 months of age, and in five healthy control infants. Nasal nitric oxide values in the primary ciliary dyskinesia infants (85 and 115 parts per billion (ppb)) were markedly lower than in the healthy controls (mean: 295 ppb, range: 225-379 ppb). This is the first report to show that nasal nitric oxide values are already low in early life in primary ciliary dyskinesia children, supporting the hypothesis that a reduced production of nasal nitric oxide is an intrinsic feature of this disease. The current authors suggest that the nasal nitric oxide test may be a useful, noninvasive method for screening young children for primary ciliary dyskinesia in clinical practice.