Recent reports have shown that low nucleated cell dose significantly decreases survival after cord blood transplantation. Prior to starting clinical cord blood banking we investigated the impact of obstetric factors on cell dose and volume of cord blood donations. Cord blood was obtained from 114 normal full-term deliveries. Mean volume collected was 93.5 ml, mean total nucleated cell count (TNC) was 13.1 x 108. Statistical analysis was by backwards stepwise regression. Significant factors affecting nucleated cell yield were volume of blood collected (P < 0.001), length of gestation (P < 0. 0001), time from delivery of the infant to cord clamping (P = 0.018) and total length of labour (P = 0.002). In clinical cord blood banking we have successfully used these findings for pre-collection assessment of placentae. Out of 476 cord blood donations subsequently collected for banking, only 29 (6.1%) have been discarded due to low volume. The mean TNC of the 409 banked units following volume reduction was 10.1 x 108. Despite careful optimization of collection, processing and storage techniques, cell dose still limits cord blood transplantation to smaller recipients.