Efficient block coding methods for LPC information play an essential role in very-low-rate speech coding systems. The subject of this contribution is a suboptimal matrix quantization scheme for LPC parameters, called matrix product quantization (MPQ), operating at bit rates between 300 and 750 b/s. In fixed-rate coding systems for mobile communication, MPQ achieves a very high coding efficiency at a low coding delay. Moreover, this paper shows that MPQ is an excellent candidate for mobile speech communication systems in terms of complexity and bit error sensitivity.