Do you mean like the following? http://finance.yahoo.com/q?s=@^nbi&f=snlcvi This shows the components of the Nasdaq Biotech Index
Each exchange gives the components of their indices: http://www.amex.com/ - pick the sector in the sector search window. http://www.phlx.com/products/sectors.html http://dynamic.nasdaq.com/dynamic/NonNASDAQActivityPrompt.stm Another good resource for sector descriptions is: http://www.bullsector.com/ Charles