A technique is described for measuring the propagation velocity of a mechanical pulse along a muscle. The pulse is generated and detected by piezoelectric crystals (bimorph benders). Measurement of the time delay for a known crystal separation gives the propagation velocity v (of the order of 100 m s-1) from which the Young's modulus is calculated. Primary results for elastic moduli of frog and toad muscles at 5 degrees C are: 2.6 X 10(6) N m-2 at rest, 3.1 X 10(7) N m-2 in tetanus and 2.1 X 10(7) N m-2 in rigor. Exploratory experiments are also described showing the application of the technique to (i) the development of tetanus, (ii) variation with sarcomere length and (iii) the mechanics of rigor. The pulse technique gives an almost instantaneous measurement of the purely elastic response of a muscle and is thereby of value in basic studies of the mechanism of contraction. It is also a useful non-destructive probe in following the effects of such variables as temperature, fatigue or chemical treatments.