Abstract The fields generated by “quarks” in the adjoint representation of SU(2) color are analyzed in the scaling region of the four-dimensional lattice theory. Evidence of vacuum screening of adjoint quarks is obtained from a comparison of quark-antiquark ( Q Q ) flux-tubes for quarks in the adjoint (“isospin” j = 1) and fundamental ( j = 1 2 ) representations. The component ε j of the color-electric field strength in the direction parallel to the Q Q axis is calculated. Near the quarks the ratio of fields ε j=1 ε j= 1 2 approaches the value 8 3 , which is equal to the ratio of SU(2) Casimirs. In between the quarks, the ratio falls well below 8 3 at large R. ε j also falls off rapidly as a function of distance x ⊥ perpendicular to the Q Q axis. However, the ratio ε j=1 ε j= 1 2 depends very weakly on x ⊥. The flux-tubes in the two representations thus appear to have very similar cross-sections. This result could imply that the QCD vacuum is dual to a type I superconductor.