The continued development of a computerised system for measuring the pattern of the antepartum fetal heart rate (FHR) is described. Previous work had established that measurement of FHR variation objectively detects chronic fetal hypoxaemia and the onset of metabolic acidaemia antepartum. The normal centiles were calculated for the amplitude of long-term FHR variation, in episodes of high and low variation, week by week from 24-42 weeks gestation. Reference to these (automatically by the computer) improved discrimination between normal and questionable records in 38% of records, with a small saving of time. Two types of sinusoidal rhythm were described (slow, 1 in 2-5 minutes, incidence 0.16% of subjects; and faster, 2-5 per minute, incidence 0.025%) with methods for their detection. Both may be of sufficient amplitude to induce an episode of high FHR variation. The different effects of maternal steroid (betamethasone or dexamethasone) administration of FHR variation were compared, and the clinical consequences considered. The frequency distribution of basal FHR in normal and abnormal records was measured, and the effects on basal FHR outside the normal range (120-160 bpm) on FHR variation described. Adjustment of the FHR baseline was undertaken when, exceptionally, large abrupt changes in heart rate occurred during a record. The duration and frequency of FHR record acquisition in clinical practice were reviewed, and new policies recommended. With adequate safeguards, measurement by a computer offers reliable objective information from which fetal health may be assessed, more objectively and accurately than by visual inspection.