Strictly alternating polyesteramides consisting of 1,4-butylene terephthalamide and aliphatic diols have been synthesized in the melt in the presence of a titanium catalyst. The influence of diol length on the thermal and mechanical properties was studied. Depending on its structure, the diol took part in the crystallization. All polymers crystallized very fast (T-m - T-c < 33 degrees) and had a lamellar structure. The melting and glass transition temperatures decreased with increasing diol length, and both showed an odd-even effect. The polyesteramides were melt processed and their mechanical properties were determined using torsional (d.m.t.a.) and tensile tests. The polymers have a high glass transition temperature. The polyesteramides have a flexural modulus close to those of polyamides (2.9 GPa), whereas the water absorption is close to the values of polyesters (1.6 wt%). Loss of the alternating structure of the polymers, caused by ester-amide interchange reactions, was studied through C-13 n.m.r. It was found that the melting and glass transition temperatures decreased with increasing loss of uniformity.