The thigh muscles of New Zealand White (NZW) rabbits are frequently used in experimental surgery, particularly for evaluation after reinnervation or ischaemia. Although histomorphometric analyses are regularly performed, morphological data for untreated thigh muscles in previously unoperated animals are not available. Specimens from the rectus femoris (RF), vastus medialis (VM) and adductor magnus (AM) muscles from both thighs were harvested in 7 untreated rabbits and were processed for histomorphometric evaluation. The right RF and VM were harvested in a further 5 rabbit hindlimbs after experimental denervation and reinnervation of the contralateral RF and subsequently processed for histomorphometric analysis. Muscle fibre type distribution, diameter and connective tissue content were evaluated on serial transverse cryosections reacted for ATPase and NADH tetrazolium reductase activity and statistical analysis was performed. In all untreated animals RF revealed the highest proportion of type I muscle fibres (right: 8.4+/-4%, left: 11.4+/-4.9%), whereas VM showed the highest percentage of IIa fibres (right: 31.9+/-5.5%, left: 28.3+/-7.8%) and AM the highest proportion of IIb/d fibres (right: 80.5+/-8.6%, left: 84.4+/-6.3%). Fibre type distribution and diameter in rabbits after contralateral experimental operations revealed a statistically significant difference from the data obtained in bilaterally untreated animals. Knowledge of the morphology of untreated muscles is fundamental to the understanding of changes induced by intervention to the ipsi and/or contralateral thigh muscles.