Dielectric permittivity has been measured for mixed crystals K1-x(NH4)(x)H2PO4 (KADP) and Cs1-x(NH4)(x)H2PO4 (CADP) and its deuterated analog (DCADP), as well as for two parent crystals, ferroelectric CsH2PO4 (CDP) and antiferroelectric NH4H2PO4 (ADP). The measured response contains two components, the dielectric response associated with the ferroelectric or antiferroelectric behavior, and the protonic conductivity response which is the subject of this report. Both normal and anomalous features are seen in the protonic conductivity. The normal c-axis conductivity for CADP is characterized by activation energies ranging from 0.56 eV for CDP to 0.32 eV for CADP.4 (40 mol.% NH4 in the growth solution, about 0.06 mol.% in crystal), so ammonium admixture increases the conductivity but decreases the activation energy. Deuteration has little effect, at least on the c-axis conductivity. The conductivity is anisotropic, and considerably larger along the ferroelectric b axis than along a or c. The most important anomaly is a large hump in conductivity in the 210 K to 270 K range for both CADP and KADP, about 20 K wide. Heating runs in CADP produced much larger and more irregular anomalies than cooling runs. These anomalies could be nearly eliminated by applying a de bias field. The KADP runs did not extend far enough above the humps to determine whether, or where, normal protonic conductivity sets in.