Short-term heart rate and blood pressure variability were assessed in 62 patients, studied within 1 month, at 1, at 2 or at 3-5 years after cardiac transplantation and in 13 healthy control subjects. Means and total variances were calculated and the powers of the low frequency (LF, 0.07-0.14 EqHz) and of the high frequency (HF, 0.14-0.35 EqHz) components were derived from power spectral analysis. Mean heart period, its total variance and the powers of the LF and HF components were lower in the transplanted patients than in the controls (P < 0.001). The total variance and the LF and HF powers differed significantly among the groups of transplanted patients (P < 0.01) and intergroup comparison showed significantly higher values in patients 3-5 years after transplantation than in those studied within 1 month. The variance of systolic blood pressure and its power spectrum did not differ between patients and controls. The results suggest that partial functional reinnervation of the sinus node occurs after heart transplantation in man.