We describe a design for high-gain DC bioamplifiers with automatic offset nulling capability. Taking advantage of state-of-the-art commercially available linear integrated circuits, the design is suitable for low-level measurements such as EEG and event-related potentials. DC input offsets can be nulled instantly, making multichannel DC amplification feasible without time-consuming manual offset compensation. In addition, both signal and DC offset outputs are provided, permitting concurrent monitoring of slow large-scale DC shifts as well as faster small-signal activity . An alternative AC mode with signal and offset outputs is also provided. This approach lends itself to a wide range of applications in which small DC biopotentials must be measured in the presence of larger, variable DC components.