The effects of microinjections of D1 selective dopaminergic substances into the medial frontal cortex (MFC) on information storage and proactive interference during delayed (the deay in 3s) and non-delayed choice in Y-maze were studied. Bilateral micromjection of D1 receptor antagonist SCH 23390 (1 nM, 1 μ1) impaired both delayed and non-delayed choice. In contrast, microinjections of D1 receptor agonist SKF 38393 (1 nM) into the MFC significantly improved the delayed peformance and did not influence the non-delayed choice. The effects of proactive interference caused by SCH 23390 and SKF 38393 injections were more pronounced in delayed choice condition than in the non-delayed task. Spatial bias in animal behavior was revealed after the SCH 23390 injections: during erroneous choices rats more frequently turned in the same direction as preferred in a rotation test. The results suggest that impairment of delayed performance in Y-maze observed under the blockade of D1-mediated neurotransmission in the MFC occurs due to enhancement of the processes of proactive interference and disinhibition of the spatial set.