In order to provide data for process modeling, work-hardening and rate-sensitivity coefficients of the first and second order were determined for oxygen-free, high-conductivity copper and 99.99 percent aluminum. For this purpose, tension tests were carried out at room temperature and with constant rates of deformation varying from 5 × 10⁻⁴ to 1 s⁻¹. In each test, a constant true strain rate was applied at the minimum cross-section of specially machined samples by means of a computer-interfaced, servo-controlled hydraulic testing machine. The work-hardening coefficient, H = (∂ ln σ/∂ε)_˙ε, the rate sensitivity of the work-hardening rate, B_σ = (∂H/∂ ln ˙ε)_σ, and the curvature term, C = −(∂H/∂ ln σ)_˙ε, were determined from the flow curves of continuous tests. By performing strain rate changes at constant structure τ and measuring the immediate stress changes, the “instantaneous” rate sensitivity, M = (∂ ln σ/∂ ln ˙ε)_τ, was also established. The dependence of the coefficients derived in this way on stress and strain rate is described. From the variation of M with σ and ˙ε, the coefficients P = −(∂M/∂ ln ˙ε)_σ and Q = (∂M/∂ ln σ)_˙ε were evaluated. It was determined that an additional strain of 0.2 had to be imposed on the sample to take it from the UTS condition (H = 1) to the condition H + B_σ = 1. The latter is associated with the onset of flow localization, and the additional strain of 0.2 is a measure of the retarding effect of B_σ on the flow localization process. To assess the effect of impurities, a Haasen plot (M_σ versus σ) was constructed, which indicated that the copper was solution hardened due to the presence of ≅200 ppm of Ag + Mg + S, while there was no effect of solutes in the aluminum.