Allows to bring some order to the system of short interspersed elements (SINEs) and to set a basis for further studies on these genomic elements. SINEBase introduces a set of formal definitions about SINEs. More than 170 families have been counted (concerning animals, flowering, plants, and green algae) on the base. These families are classified according to the modular structure of their nucleotide sequences. The website can be used in two ways: (1) exploring the database, (2) analyzing candidate SINE sequences.