STRAP: Interactive Structure based Sequences Alignment Program. The free computer program Strap aligns proteins by sequence and 3D-structure und Windows, Macintosh, Linux and Unix. Run the demo showing 6 sequences of the proteasome within a secure Strap session. Strap supports the simultaneous analysis of hundreds of proteins and integrates amino acid sequence, secondary structure, 3D-structure and genomic- and mRNA-sequence and residue annotation. Snapshot of the Strap application. Bottom panel: Multiple sequence alignment in Strap. Four proteins are selected and conserved amino acids are colorized according to chemical property. Top panel: One of the proteins is shown in 3D. screenshot The alignment can be exported and modified in MS-Word or other text processors. Import and export of proteins is very easy by WIKI:Drag-and-Drop. The included tutorial will teach the use of Strap in as little as one hour. The scriptability and extendability make Strap a very powerful tool for even the most advanced users. The software programmed in Java and runs on all platforms. It will be permanently improved.