Abstract: Method and apparatus for monitoring curing in a resin. Acoustic, ultrasonic waves are propagated through a waveguide disposed through a quantity of resin while the resin is curing. The waves are transmitted and received by transducers arranged in an acousto-ultrasonic configuration with respect to a flexible waveguide. The waveguide may be made from bundled fibers. The velocity or amplitude of the acoustic waves is affected by the physical characteristics of the resin sample. Monitoring changes in the speed or amplitude of the propagated waves permits changes in the resin to be monitored in real time. Only a small sample quantity of resin need be employed.