High-speed photography and impaction cards have been used to enhance knowledge of the manner in which droplets of Newtonian and non-Newtonian fluids break up in a high-speed jet of air. The photographs show that breakup was initiated for both types of fluid by the formation of waves on the surface of droplets exposed to the air stream, with frequency which depended on the velocity of the air jet, and with bags ill the low-velocity regions behind the droplet and downstream of the peaks of the wave. The waves were subsequently stripped to form ligaments, initially joined by bags to form a web of ligaments and later separated into two parts as their central regions stretched and droplets were formed within a distance of 20 diameters of the original droplet. The non-Newtonian fluids have been categorized in terms of critical speed of breakup which increased with the addition of a copolymer to a critical velocity of 540 m/s. It is likely that higher concentrations of the copolymers than those examined here will lead to higher critical velocities, Additional experiments established that initial droplet diameters from 2 to 4 mm and the height from which the droplet fell into the air stream, 20 mm to 1 m had little effect on the critical speed.