The morphology of primary afferents to the spinal cord of the turtle Pseudemys scripta elegans was studied by means of intra-axonal injections of horseradish peroxidase. A total of 74 collaterals arising from 34 different afferents in 22 animals was investigated. Within this sample, a division into three morphologically distinct collateral types appeared possible. Collaterals of the same parent axon could always be classified to the same type. Type A collateral arborizations could be found within area I-II and III of the spinal grey matter. The number of presynaptic boutons per collateral varied considerably. However, collaterals of the same parent axon usually possessed a similar general appearance. Type B collaterals terminated within area IV and V-VI. The general shape and number of boutons could differ considerably between collaterals of different parent fibers but also between collaterals of the same axon. Type C collaterals formed terminal arborizations in the lateral parts of areas IV, V, VI and VII-VIII and demonstrated a fair constancy in general appearance and number of presynaptic boutons. Type A collaterals are thought to be derived from fibers innervating various cutaneous receptors. Terminal arborizations of type C collaterals are fully overlapping with the dorsal dendritic trees of turtle lumbar motoneurons. It is suggested that type C collaterals form contacts with these motoneurons and arise from muscle spindle innervating afferents. The origin of type B collaterals is less clear, attractive possibilities may be found in joint and/or tendon organs.