The paper presents the analysis of the side-chain conformation angles of amino acids in 90% non-identical protein structures. The analysis has been carried out using 113,699 residues, which is higher compared to the previous studies. In the present study, one more quality check, namely, temperature factor cut-off, has been introduced in addition to resolution and R-factor cut-offs. Due to this, the present calculation reveals the approximate values for the minimum and the maximum of the three-rotameric states of chi(1). In addition, the conformation angles chi(2) and chi(3) have been addressed with the improved data set. The results reported here could be of use in protein modeling. (C) 2003 Elsevier Inc. All rights reserved.