The design, calibration, and operation of a source of controlled amounts of cyclic AMP (c-AMP) are described. Typically, 1.5 s pulses containing 10(10)-10(-12) molecules of c-AMP can be delivered to a region about 10 mum in diameter on an agar plate. The resulting concentration profiles are given as functions of distance and time. The diffusion coefficient of c-AMP in agar was measured to be 0.97 times 10(-5) cm2-s-1 at 21 degrees C.