This book constitutes the refereed proceedings of the International Symposium on Knowledge Exploration in Life Science Informatics, KELSI 2004, held in Milan, Italy in November 2004.The 20 revised full papers presented were carefully reviewed and selected for inclusion in the book. Among the topics covered are proteomic data analysis, rule induction, multiple sequence alignment, pattern extraction, microarray analysis, functional data analysis, text mining, artificial life, evolutionary algorithms, randomized algorithms, feature extraction, classification, case-based learning, and bioscience education.