Sixty adult pigeons of two breeds (Carrier & Baladi) were selected for the experimental purposes. This work was done to investigate some physiological and histological basis of learning behaviour & intelligence and the effect of iron administration on discriminative behaviour. The obtained results indicated that the brain weight / body weight ratio was significantly higher in Carrier pigeons than that of Baladi and iron- treated Baladi ones. There was a significant increase of dopamine and norepinephrine and a decrease of serotonin and 5-hydroxyindoleacetic acid contents in Carrier pigeons than those in Baladi and iron-treated Baladi ones. Also it was found that plasma and brain iron concentrations of Carrier pigeons were significantly higher than those of Baladi and iron - treated Baladi ones. There was a significant reduction in the number of trials after which the Carrier pigeons start to elicit the response.