Of 54 milk samples from 54 healthy nursing women analysed for volatile N‐nitrosamines, 42 appeared negative. Trace amounts (below the detection limit 0.5 μgl−1) of N‐nitrosodimethylamine were detected in the milk of 10 mothers and two samples contained this compound at 1.1 and 1.2 μgl−1 respectively. Almost all samples investigated contained nitrate (mean 2.9 ± 2.3 mgl−1) and nitrate reducing microorganisms (mean 4.2 ± 1.0 log ml−1). The recent finding of N‐nitrosodimethylamine in human milk gives evidence of the continuous endogenous formation of N‐nitrosamines.