In the BMJ of 18 April 1992, we published a paper by Ram B Singh, Shanti S Rastogi, Rakesh Verma, B Laxmi, Reema Singh, S Ghosh, and Mohammad A Niaz (1992;304: 1015-9). We now wish to express concern about the validity of this paper. This expression of concern is based on investigations the BMJ has carried out into the work of the paper's lead author and what has emerged about it and its reliability in the course of these investigations. An account of these investigations is published on page 281.1 As a result of these investigations, we have reasonable grounds to doubt the validity of the 1992 paper.