Studies of locomotor patterns of fusimotor activity in decerebrate cats have been hampered by the need to denervate one hindlimb extensively and to restrict movement to rotation of the ankle joint (Taylor et al. 2000 a,b). It is important to know whether the consequent loss of natural afferent input affects the normal activity patterns. Here we compare this earlier data with new recordings from single spindle afferents of ankle flexor and extensor muscles with no significant denervation and with all limbs walking freely on the treadmill. Cats (n = 13) were anaesthetised with 2% halothane in 50% nitrous oxide in oxygen (as previously described (Taylor et al. 2000 a) until after premammillary decerebration and killed at the end of the experiment with pentobarbitone overdose. Strain gauges recorded the lengths of tibialis anterior (TA) and gastrocnemius muscles and EMG electrodes were inplanted. Cats were supported by a head holder, a clamp on a low thoracic vertebra and by pins in the iliac bones. The thoracic and pelvic supports were free to move vertically and hung from springs. A small dorsal root filament of L7 or S1, exposed through a left-sided laminectomy was dissected on a floating electrode platform sutured to the vertebrae. Single spindle afferents were isolated from gastrocnemius, soleus or TA and stable recordings from up to 6 units could be achieved. They were characterised by the effects of succinylcholine and by conduction velocity measured under full sodium pentobarbitone anaesthesia after the locomotor recordings. Muscle length changes recorded on tape during walking were reproduced later with a servo, with fusimotor activity suppressed by pentobarbitone. Natural fusimotor activity was deduced from the difference in spindle firing in active and passive spindle movements. The free limb showed movements very similar to those found in intact cats walking on a treadmill (e.g. Bélanger et al. 1996). EMG bursts in gastrocnemius were more prolonged than in the fixed limb and this corresponded to the stance phase and weight bearing. Despite this difference the active minus passive spindle firing indicated very similar static fusimotor patterns, with firing frequency matching muscle shortening and with phase advance of 0.1 cycle length. In TA, static fusimotor patterns also appeared to match muscle shortening and with similar phase advance, in contrast to the fixed limb, which showed no phase advance in TA.