George Johnstone Stoney, Lord Rosse's assistant, discovered NGC 4399, along with NGC 4400, on 13 Apr 1850, while observing NGC 4395. On 14 Apr 1855, R.J. Mitchell noted "there are 4 nebulae. The 3 following ones seem to be involved in a mass of faint nebulosity. A sketch shows 4 "nebulae" along with a couple of stars. One of these (furthest north on the sketch) is the core of NGC 4395 and the other three (NGC 4399, NGC 4400 and NGC 4401) are HII knots in the galaxy. John Herschel recorded NGC 4401, the brightest of the knots.

Francis Pease assigned NGC 4399 to the knot identified here as NGC 4400 in his 1920 paper on nebulae photographed with the Mt Wilson 60-inch. Corwin lists the position for NGC 4399 as 12 25 42.8 +33 30 57, which is just following a mag 15 star. RNGC classifies the number as nonexistent with the description "Part of NGC 4395."

400/500mm - 17.5" (5/15/99): faintest of three HII knots observed in NGC 4395. Appeared extremely faint and small, 10"-15" in size and situated 2.3' SW of the ill-defined core on a line with a mag 14.5 star to the NE of the core. Required averted vision to confirm.

Notes by Steve Gottlieb