Objective: Scientific studies include references to historical studies on low-level laser therapy (LLLT) in general and to old studies on the specific subject in particular. Some studies are quoted often. It is fair to take a second look at these, since few people seem to have read them carefully, and others have read them only in the abstract form. This paper critically reviews the parameter pitfalls found in many of the classic "negative" studies.
Summary background data: A study of 1,200 papers on LLLT has resulted in 85 positive and 35 negative double-blind studies. The negative studies have been scrutinized carefully in an effort to pinpoint possible reasons for the failures. In the following, the majority are double-blind studies, but some non-blinded and animal studies have been included to give typical examples of pitfalls.