A fiber-optic chaos communication system for allowing bidirectional message transmission is first constructed and experimentally demonstrated. Using the synchronized chaos outputs of two authorized semiconductor lasers as communication carriers, two oppositely transmitted high frequency analog messages (3 and 4 GHz) can be encrypted and decrypted between two communication terminals over a 10-km single mode fiber channel. Furthermore, two data streams with bit rates of 2.5 Gb/s can also be bidirectionally encrypted and decrypted with bit-error-rates estimated below 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> .