A load modulated multiple-input multiple-output (MIMO) transmitter uses a single central power amplifier and tunes the antenna loads according to the information signal, eliminating the need for traditional radio frequency (RF) chains (consisting of DACs, mixers, and filters) at the transmitter. In this letter, we consider the use of load modulation (LM) in multiuser MIMO communication on the uplink. Multiple user terminals, each using an LM array (e.g., with 2 or 4 antenna elements), communicate with a base station with multiple receive antennas. First, considering small systems using maximum-likelihood detection, we show that multiuser LM outperforms single-RF chain multiuser systems that employ conventional modulation and spatial modulation. Next, in order to scale multiuser LM to large systems, a low-complexity detection algorithm based on message passing is proposed. The performance of large-scale multiuser LM systems achieved using the proposed algorithm is shown to be better than that achieved in large-scale multiuser systems that employ conventional and spatial modulation.