Electronic measurements of compression, using a hydrostatic technique, were made during 44 normal deliveries and compared with the values obtained during 32 deliveries using Kielland's forceps, 21 using Neville Barnes' forceps, 48 using Moolgaoker's adjustable forceps, and 26 using Malmstrom's vacuum extractor. Electronic recordings of traction, using strain gauges, were made simultaneously during all the instrumental deliveries except those with Kielland's forceps. By exercising suitable controls over most of the multiple factors operating at the time of any delivery the authors were able to compare objectively the efficiency of the different methods of instrumental delivery. Smaller forces of compression and traction were exerted and better Apgar scores were recorded in infants delivered with the adjustable forceps than in infants delivered with the other instruments. The superiority of the adjustable forceps was most noticeable during midcavity deliveries of the malrotated head.