The direction of the cyclocondensation of 2-fluoro-5-nitrobenzaldehyde with five amidines having α-hydrogen atoms has been studied. It was established that depending on the structure of the amidine the main products of the reaction may be not only quinazolines but also 3-aminoisoquinolines. A new convenient route has been found for the synthesis of 3-aminoisoquinolines consisting of the cyclocondensation of α-acylacetamidines with 2-fluoro-5-nitrobenzaldehyde.