In order to understand elongator tRNA(Ser) and suppressor tRNA(Sec) identity elements, the respective acceptor-stem helices have been synthesized and crystallized in order to analyse and compare their structures in detail at high resolution. The synthesis, crystallization and preliminary X-ray diffraction results for a seven-base-pair tRNA(Ser) acceptor-stem helix are presented here. Diffraction data were collected to 1.8 A, applying synchrotron radiation and cryogenic cooling. The crystals belong to the monoclinic space group C2, with unit-cell parameters a = 36.14, b = 38.96, c = 30.81 A, beta = 110.69 degrees .