A previously unpublished room painting depicting 'Saint Jerome in Meditation', which emerged without any attribution from a private collection north of the Alps, is attributed by the present author to a prominent exponent of 17th-century Italian painting, Guido Reni. The arguments put forward to confirm the attribution and the late dating of this new and very high quality work have provided the opportunity for further reflections concerning Guido's so-called “seconda maniera”, raising questions moreover regarding the “non-finito” which characterized the painter's later production, a topic of considerable interest and various interpretations on the part of art scholars at least from the middle of the last century onwards.