A full binary adder utilizing a single tunnel diode and three resistors as its basic components is described, the circuit design criteria is outlined and values for a typical case are computed. The operating rate of the adder was determined analytically to be approximately 3 nsec. Experimental results obtained with a practical circuit that employed a 1N2939 tunnel diode were in good agreement with the analytical findings. The Sum and Carry outputs were 130 mv and 300 mv, respectively. These outputs need to be amplified if used to drive identical stages since there is no gain in this circuit. Since a full binary adder is a multipurpose logic element, a simple, compact, full binary adder that contains few components presents attractive possibilities for new computer logical schemes. This adder offers circuit simplicity and stability and is particularly suitable for application where low-power dissipation and compactness are desired.