We have measured the amplitude of ocular counterrolling (OCR) and the change in vertical deviation in the Bielschowsky head-tilt test (BHT) in 23 cases of unilateral superior oblique palsy. OCR was measured with a photographical method, using limbal, conjunctival vessels as landmarks. Average OCR of the healthy eye was 5.4 +/- 2.4 (SD) deg either side, at 45 deg of body-tilt. BHT and OCR (of the healthy eye) were not related in the group as a whole. An important perturbing factor was the duration of the palsy. To clarify the relation between BHT, OCR and duration of palsy, the BHT/OCR ratio was calculated in each patient. Six cases with a palsy of presumed recent onset had BHT/OCR ratio of 0.57 +/- 0.09, while twelve cases of long-standing palsy had a BHT/OCR ratio of 1.04 +/- 0.71. This means that in cases of recent onset, the relation was relatively fixed. All high BHT/OCR ratio's occurred in long-standing palsies, whether acquired or congenital. In our opinion, disproportionately large amplitudes in the Bielschowsky head-tilt test are caused by secondary innervational changes or contractures.