The signal recognition particle database (SRPDB) is located at the University of Texas Health Science Center at Tyler and includes tabulations of SRP RNA, SRP protein and SRP receptor sequences. The sequences are annotated with links to the primary databases. They are ordered alphabetically or phylogenetically and are available in aligned form. As of September, 1998, there were 108 SRP RNA sequences, 83 SRP protein sequences and 28 sequences of the SRP receptor alpha subunit and its homologues. In addition, the SRPDB provides search motifs consisting of conserved amino acid and nucleotide residues, and a limited number of SRP RNA secondary structure diagrams and 3-D models. The data are available freely at the URL http://psyche.uthct.edu/dbs/SRPDB/SRPDB.++ +html