  We present a photoacoustic resonant cell, the internal volume of which is ~
0.5 cm^3. The cavity shape of the cell is so adapted in order to minimize the
background signal arising due to absorption of laser beam in the cell windows.
An experimental setup, measurement procedure and design of the cell are
described. Results of detection of ammonia in nitrogen flow with the help of a
CO2-laser are represented. The minimal detectable absorption for the cell is
estimated in the experiment to be ~ 5.1 10^(-8) cm^(-1) W Hz^(-1/2)
