Spatial multiplexing techniques in multiuser multiple-input multiple-output orthogonal frequency- division multiplexing (MU-MIMO-OFDM) systems have increased the spectral efficiency of wireless communications systems. However, these systems require an accurate knowledge of the channel at the transmitter, which usually has to be provided by receivers through a low-rate feedback channel. In this paper, we present a channel quantization scheme based on the Karhunen-Loève (KL) transform. This scheme outperforms the scheme based on time-domain quantization in terms of mean square error for a given amount of quantization bits. The comparison has been carried out in a system that presents some unmodulated subcarriers. The computational complexity of both schemes has also been analyzed showing that, when efficient eigendecomposition is used, the scheme based on KL transform has only a slightly higher computational complexity.