The targets and afferents of the cat''s midbrain reticular core were investigated in chronically implanted, behaving animals. Antidromically and synaptically elicited discharges were extracellularly recorded in single neurons. Neurons (97 of 408; 23%) were antidromically excited from outside the midbrain, including the medial intralaminar thalamic nuclei, zona incerta and median-paramedian pontine fields. The axons projecting toward these 3 main regions were homogenously slow conducting (median, 3.5-4.6 m/s). Only 8% of the identified projecting neurons had either bifurcating axons in 2 rostral directions or an ascending and a descending branch. There was no indication that neurons were differentially localized with respect to the site of projection. The analysis of synaptically evoked responses with latencies under 20 ms (mostly between 1 and 5 ms) revealed that 33% of neurons (n = 137) were selectively excited from a single site and 22% (n = 91) from 2-4 sites. Of all synaptically responsive neurons, 82% were driven from the medial thalamus, subthalamus or pons. These sites were the most effective in inducing antidromic responses. Only occasionally was antidromic invasion of a neuron accompanied by its synaptic activation from the same site. Cells that had axons projecting to structures outside the midbrain had sparse synaptic input from these structures; synaptic input was very frequently seen in cells not antidromically excited.