The birth weights of 13,351 babies born at full term from 1964-84 to Asian Moslem mothers in Birmingham were analysed to see if the effect of the Ramadan fast on maternal biochemical profiles was of any clinical relevance. These were compared with two age matched control groups comprising white and non-Moslem Asian babies. Ramadan had no effect on mean birth weight at whatever stage of pregnancy it occurred. There was an increase in the prevalence of low birth weights (4.5% to 8%) among babies who were born at full term when Ramadan had occurred during the second trimester, but this was not significant. We conclude that the Ramadan fast has no effect on the birth weights of babies born at full term.