This article discusses potential problems which may arise in LSD sentence modification proceedings, some of which are specific to that amendment and others which would be involved in any sentence modification pursuant to section 1B1.10 of the Sentencing Guidelines (SG). The author suggests that by making a significant change to section 1B1.10, many of these problems would be eliminated. Section 2D1.1(c) of the SG was amended in 1993 to provide a different means of computing the weight of LSD. This amendment will generate markedly lower sentences for LSD cases than were generated previously, using the actual weight of the LSD and carrier medium. In addition, this amendment is retroactive. The Sentencing Commission estimates that there have been approximately 400 defendants sentenced pursuant to the previous computation guideline. It is likely that more motions for modification of sentences will be filed based on this amendment than any other retroactive amendment to date. Issues raised by the amendment are considered including the dose computation, application of the amendment's weight formula in light of the holding in Chapman v. United States, 111 S.Ct. 1919 (1991), and the "whole-book" or "one-book" approach for implementing a retroactive amendment. The author explains that the use of the current set of guidelines, i.e., the whole-book approach, rather than simply using the retroactive guideline in the context of the set used at sentencing, allows new factual issues to complicate the sentence modification, which in turn generates several procedural concerns. The role of the probation officer in a sentence modification proceeding is explored. The author urges a reconsideration of the use of the whole-book approach, concluding that this approach is best supported by the preservation of the original full set of guidelines used at sentencing, with only the retroactive amended guideline inserted therein, effecting a more specific, "laser-beam" kind of modification of the original, otherwise coherent, sentence. Statutory authority also suppports this position. Notes