Abstract: A steganographic method is proposed for embedding secret information in digital speech signals. Depending on the PCM A/ law compression/decompression characteristics and mutual conversion between the two laws, appropriate bit planes are chosen in modifying the host speech samples to embed secret data. The induced distortion is highly imperceptible, and the embedded information is robust against A/ law compression and mutual conversion, therefore suitable for transmission not only through the Internet but also through international PSTN. Experimental results indicate the effectiveness of the proposed method.