This table lists the number of members of WS-I since its inception.
| Date | Members |
| February 1, 2003 | 149 |
| April 15, 2003 | 151 |
| June 18, 2003 | 145 |
| February 17, 2004 | 138 |
| March 25, 2004 | 132 |
| April 13, 2004 | 127 |
| May 17, 2004 | 123 |
| July 16, 2004 | 118 |
| September 22, 2004 | 124 |
| November 3, 2004 | 121 |
| October 25, 2006 | 83 |
FWIW, I assume that the decrease in that table in early 2004, is due to acquisitions and failed startups.
As of 2006, their Web site has changed and it no longer seems possible to automate the count.