http://members.westnet.com.au/pkolb/doc-A4G.pdf - Buteyko Guide for Doctors, by Peter Kolb BSc(Eng), BSc(Med), Biomedical Engineer. This is a brief, clear, accurate description of the Buteyko method and of the role of Buteyko practitioners. Read this for a good overview. It has many references at the end.
http://www.nzma.org.nz/journal/116-1187/710/ - New Zealand Medical Journal report on double blind study assessing impact of Buteyko Breathing Technique on medication used in asthma.
Buteyko: A useful tool in the management of asthma? - This article explains the aims of Buteyko and discusses the increasing evidence base for methods that reduce ventilation and may benefit many patients with asthma, not just those with established chronic perventilation.
Hyperventilation Syndrome: A Diagnosis Begging for Recognition by Gregory J. Magarian, MD; Deborah A. Middaugh, MD and Douglas H. Linz, MD, Portland from "Topics in Primary Care Medicine"
http://www.buteyko.ru/eng/index.shtml - The Russion Buteyko clinic's website.