Prijatelj's efforts answered many unsolved topics in Dalmatian art history.

Prijatelj was the most important Croatian scholar of his generation in Dalmatian art history, particularly in the Baroque period.

He wrote about the figures of Dalmatian art, and rediscovered lesser-known artists such as Matteo Ponzone.

He attributed several works to Biagio di Giorgio da Traù [it], an itinerant Italian painter with scattered works between Zadar, Trogir, Split, Dubrovnik, Ston and Čiovo.

Beginning in 1972, he taught contemporary art history at the Faculty of Philosophy in Zagreb, as adjunct professor.