To investigate whether valid respiratory data could be extracted from the pulse oximeter plethysmographic (pleth) trace in healthy newborn infants, we collected pleth data from the foot and simultaneously measured respiratory airflow using a facemask. The pleth waveform was analysed using Fast Fourier Transform (FFT), low pass filtering (LPF), and by plotting the peak-to-peak amplitude variation (PtP). Using FFT in 14 term infants, median (range) respiratory rate from the pleth signal was 43 (30-65) and from the flow signal 44 (30-67) breaths/minute (median difference 0.01 breaths/min, p>0.05). Both LPF and PtP analysis yielded waveforms with a frequency similar to respiratory rate. Respiratory information, including respiratory rate and a respiratory-like waveform, can reliably be extracted from the pleth trace of a standard pulse oximeter in newborn infants. Such analysis may be clinically useful for non-invasive assessment of respiratory problems in infants and young children.