AGREEMENT Pursuant to Rule 13d-1-(k)(1) under the Securities Exchange Act of 1934, the undersigned hereby agree that only one statement containing the information required by Schedule 13G need be filed with respect to the ownership by each of the...

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CUSIP NO. 00000000                  13G                    PAGE 12 OF 16 PAGES
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                                                                       Exhibit 1

                                    AGREEMENT

      Pursuant to Rule 13d-1-(k)(1) under the Securities Exchange Act of 1934,
the undersigned hereby agree that only one statement containing the information
required by Schedule 13G need be filed with respect to the ownership by each of
the undersigned of shares of stock of Illumina, Inc.

      This Agreement may be executed in any number of counterparts, each of
which shall be deemed an original.

Dated: February 11, 2005

                                ARCH VENTURE FUND III, L.P.

                                By: ARCH Venture Partners, L.L.C.
                                    its General Partner

                                    By:            *
                                        ------------------------------
                                        Xxxxxx Xxxxxxx
                                        Managing Director

                                ARCH VENTURE PARTNERS, L.L.C.

                                    By:            *
                                        ------------------------------
                                        Xxxxxx Xxxxxxx
                                        Managing Director

                                            *
                                -------------------------
                                  Xxxxxx Xxxxxxx

                                            *
                                -------------------------
                                  Xxxxx Xxxxxxxx

                                            *
                                -------------------------
                                  Xxxxxx Xxxxxx

                                            *
                                -------------------------
                                  Xxxxxxx Xxxxx

                                             * By: /s/ Xxxx XxXxxxxxx
                                                  ----------------------------
                                                  Xxxx XxXxxxxxx as
                                                  Attorney-in-Fact

This Agreement was executed by Xxxx XxXxxxxxx pursuant to Powers of Attorney
attached hereto as Exhibit 2 and incorporated herein by reference.

                              Page 12 of 16 Pages