Curves+, a revised version of the Curves software for analyzing the conformation of nucleic acid structures, is now available as a web server. This version, which can be freely accessed at http://gbio-pbil.ibcp.fr/cgi/Curves_plus/, allows the user to upload a nucleic acid structure file, choose the nucleotides to be analyzed and after optionally setting a number of input variables, view the numerical and graphic results online or download files containing a set of helical, backbone and groove parameters that fully describe the structure. PDB format files are also provided for offline visualization of the helical axis and groove geometry.