Background: The power of microarray analysis can be realized only if data is systematically archived and linked to biological annotations as well as analysis algorithms. Description: The Longhorn Array Database ( LAD) is a MIAME compliant microarray database that operates on PostgreSQL and Linux. It is a fully open source version of the Stanford Microarray Database (SMD), one of the largest microarray databases. LAD is available at http:// www.longhornarraydatabase.org Conclusions: Our development of LAD provides a simple, free, open, reliable and proven solution for storage and analysis of two-color microarray data.