The C-13 chemical-shift tensor principal values were measured for p-aminosalicylic acid, pyrazinamide, and isoniazid. A moderate-strength hydrogen bond between adjacent p-aminosalicylic acid molecules in the crystal was simulated several different ways in attempts to find a reasonable model of the electrostatic interactions in the crystal. Crystal lattice effects on the calculated chemical-shift tensors are treated by application of the embedded ion method (EIM). Coupling between N-14 and several C-13 atoms was included in the data analysis to provide more accurate 13C chemical-shift tensor principal values. The chemical-shift tensors are assigned with a permutative algorithm based upon the computed chemical shifts.