In particular with respect to infant nutrition knowledge of the current contents of trans fatty acids (TFA) and of conjugated linoleic acid (CLA in human milk lipids is of interest. After pre-separation by Ag-TLC 11 trans-C18:1 isomers could be quantified by GC with a mean total content of 2.40 +/- 0.60 wt% in samples from 40 German women. For the positional isomers t4, t5, t6-8, t9, t10, t11, t12, t13, t14, t15 and t16 contents of 0.02, 0.02, 0.21, 0.37, 0.32, 0.68, 0.23, 0.15, 0.18, 0.09 and 0.14 wt% were established, with vaccenic acid being the predominant isomer. Further, small trans-C14:1 and trans-C16:1 contents of 0.08% and 0.15% on average were found. As the trans-C18:1 isomers also the trans-C16:1 isomers of human milk lipids could for the first time be baseline-resolved by GC to a great extent. Moreover, besides a mean CLA (c9,t11) content of 0.40 +/- 0.09% further 6 cis/trans isomers of linoleic acid with a total content of 1.07 +/- 0.56% on average (w/o CLA) were determined. Further, 4 trans isomers of alpha-linolenic acid could be baseline-resolved exhibiting a total content of 0.11%. Altogether German human milk lipids on average were found to contain 3.81 +/- 0.97% TFA with a range of 2.38-6.03%. Direct connections between the dietary intake of trans-C18:1 isomers and the composition of human milk lipids could be established. The major fatty acids exhibited the following contents (wt%): C4: 0.16, C6: 0.18, C8: 0.06, C10: 0.58, C12: 3.12, C14: 6.43, C16: 25.28, C18: 7.41, C18: 1 (total): 33.67, C18: 2 (total): 10.63 and alpha-C18: 3:0.87.