A tool is presented that helps to find biological functions for new protein sequences. Running on any Macintosh computer system, MacPattern provides a unique combination of different algorithms, speed and user-friendliness. It supports searches for protein patterns using the PROSITE database, protein block searches with the BLOCKS database, and the identification of statistically significant protein segments. MacPattern allows batch processing of sequences and automatic translations of nucleotide sequence data. It is particularly suited for genome analysis or cDNA sequencing projects.