6.              Revenue Recognition

We present revenue from our collaboration arrangements under the FASB ASC 808, Collaboration Arrangements. Our revenue arrangements with multiple elements are evaluated under FASB ASC 605-25, Multiple-Element Arrangements (as amended by ASU No. 2009-13), and are divided into separate units of accounting if certain criteria are met, including whether the delivered element has standalone value to the customer, whether the arrangement includes a general right of return relative to the delivered element and whether delivery or performance of the undelivered element is considered probable and substantially under our control. The consideration we receive under collaboration arrangements is allocated among the separate units of accounting based on the selling price hierarchy, and the applicable revenue recognition criteria is applied to each of the separate units. Advance payments received in excess of amounts earned are classified as deferred revenue until earned.

Revenues associated with substantive, at-risk milestones pursuant to collaborative agreements are recognized upon achievement of the milestones. We consider a milestone to be substantive at the inception of the arrangement if it is commensurate with either our performance to achieve the milestone or the enhancement of the value of the delivered item as a result of a specific outcome resulting from our performance to achieve the milestone, it relates solely to past performance and it is reasonable relative to all of the deliverables and payment terms within the arrangement. Non-refundable contingent future amounts receivable in connection with future events specified in collaboration agreements that are not considered milestones will be recognized as revenue when payments are earned from our collaborators through their completion or achievement of any underlying events, the amounts are fixed or determinable and collectability is reasonably assured.