The Massachusetts Supreme Judicial Court (SJC) recently tackled the thorny question of retroactive application of an amended interpretive regulation in the context of Massachusetts‘s Abandoned Property Law (APL), and issued a significant victory to Biogen Idec MA, Inc.[1] The court rejected the state treasurer‘s attempt to narrow the APL‘s business-to-business exemption by excluding uncashed accounts payable checks through the 2004 amendment of regulations that had been issued contemporaneously with the 2000 APL legislation and that were in effect at the time of Biogen‘s 2002 amnesty filing.