The mean duration and amplitudes of the lead II electrocardiogram were determined in the peregrine falcon (Falco peregrinus brookei) using 10 birds ranging in age from 1 to 5 yr. Electrocardiograms were performed on unanesthetized falcons in order to avoid the anesthesia effect on the electrocardiogram, by a method which seems to induce a tonic immobility-like reaction. All the falcons had a normal sinus rhythm, with a mean heart rate of 268 beats per minute. Mean durations of PR, ST, QT, and RR intervals were higher (but not statistically significant) in females than in males, except for the ST segment, with similar values in both sexes. P-wave deflections were positive in I, II, III, aVL, and aVF and negative in aVR. The normal patterns of wave forms of the QRS complexes in all leads were of QS and rS types, except for aVR and aVL, which presented an R configuration. The mean electrical axis was negative, with an average of -99.9 degrees. T-wave deflections were positive in I, II, III, and aVF leads II and negative in aVR and aVL. The data collected in this study may serve as a guide for electrocardiographic monitoring of peregrine falcons.