Quantitative measurements were made on cross-sectional preparations of the distal part of the recurrent laryngeal nerve (RLN) from nine young mixed-breed horses to establish reference values for the total number of myelinated fibres, mean fibre diameter and percentage of thickest fibres (over 9·5 gm) and to delineate diameter distribution curves. The total number of myelinated fibres, mean fibre diameter and percentage of thickest fibres for the left RLN were significantly lower than those of the right RLN (P<0-005). The distribution of fibres was unimodal. The fibre diameter ranged from 1 μm to 17 μm. Approximately, 95 per cent of fibres had a diameter larger than 5 μm. © 1993.