In this study acetylcholinesterase (AChE) staining methods have been used to demonstrate the development of the prospective afferent fibres of auditory cortex in human fetuses ranging between 8 and 28 weeks of gestation. Earliest AChE positive staining was found in fetuses at 20--24 weeks in the neuropil of the marginal zone and throughout subplate layer of the auditory cortex. On the basis of this characteristic AChE staining pattern, the auditory cortex may be delineated from surrounding cortical areas. At 24--26 weeks, during intensive lamination of the cortical plate, AchE-positive reaction appears in the deep part of the cortical plate. In the oldest fetuses (28 weeks) a columnar pattern of vertical, darkly stained zones was seen in the middle third of the cortical plate. We conclude that AChE staining is characteristically distributed within cytoarchitectonic compartments and 'synaptic' layers of the developing auditory cortex. The AChE-positive layers coincide with the laminar pattern of synpatogeneis. Thus, AChE-positive reaction during development may serve as a parameter of cortical afferent (thalamic?) innervation of the auditory cortex. In addition, AChE reactivity may indicate the specific transmitter nature of the afferent fibres in the auditory cortex.