We present practical parallel algorithms using prefix computations for various problems that arise in pairwise comparison of biological sequences. We consider both constant and affine gap penalty functions, full-sequence and subsequence matching, and space-saving algorithms. The best known sequential algorithms solve these problems in Omn time and Om + n space, where m and n are the lengths of the two sequences. All the algorithms presented in this paper are time optimal with respect to the best known sequential algorithms and can use O n log n processors where n is the length of the larger sequence. While optimal parallel algorithms for many of these problems are known, we use a simple framework and demonstrate how these problems can be solved systematically using repeated parallel prefix operations. We also present a space-saving algorithm that uses O m + n p space and runs in optimal time where p is the number of the processors used.