Operant discrimination learning was analyzed in pigeons after massive telencephalic lesions. Twenty-one pigeons were divided into three groups: non-lesioned (N = 6), sham-lesioned (N = 5) and telencephalon lesioned (N = 10). Lesion surgeries were carried out before any experimental training. Learning procedures were run in the same sequence for all groups and under a food deprivation of 80% of the ad libitum weight. Successive discrimination was programmed by the alternation of red and yellow lights in the right key of a standard operant chamber: the red key was correlated with variable-ratio reinforcement; the yellow key was correlated with extinction. Sessions were run until steady-state key peck rates were obtained. The following results demonstrate discrimination learning by detelencephalated birds. Response shaping and steady-state rates required a larger number of sessions for lesioned pigeons (P<0.05). They showed increased response rates in red (26.43 +/- 2.59) and yellow (11.17 +/- 2.86) components as compared to the non-lesioned (red: 16.51 +/- 2.0; yellow: 2.02 +/- 0.64) and sham-lesioned (red: 22.84 +/- 1.77: yellow: 4.72 +/- 1.99) groups (P<0.05). These data show that telencephalic systems are not essential for operant discrimination learning but play a role in the modulation of discriminative behavior. Subtelencephalic systems appear to be functionally important for the organization and storage of learning.281010891095