02 breathing in healthy adults causes a small decrease in heart rate ( H R ) (2 ) . In healthy fulHerrn infants 02 breathing also leads to a small decrease in HR (1) . When the mother is breathing pure 0 2 , a decrease of FHR and LVA in the fetus can be observed (4) . These observations have been confirmed previously (5). Using an algori thm for Computer determination (CD) of FHR level and LVA (3), i t was the aim of this paper to study the behaviour of FHR and LVA before and during maternal 02 breathing with Computer assistance.