Both physicians and the lay public raise questions about drug excretion in breast milk. Enhanced interest is seen with the increase in the number of mothers who wish to breast feed. 'Contamination' of breast milk by drugs and environmental chemicals imposes risks, both known and theoretical, to the infant. Drug information centres and physicians find a meagre amount of knowledge on which to base recommenda- tions and the data which are available are often anecdotal or derived from single case reports. A critical look at both the nature and scope of our knowledge on this matter was undertaken...