William Herschel discovered NGC 3987 = H III-323, along with III-324 (either NGC 3993 or 3997) on 6 Apr 1785 (sweep 393) and recorded "vF, lE. Suspected another eF, about 5' or 6' nef. I was pretty sure of it." His single position is 2' west of UGC 6928.

In the NGC, Dreyer mistakenly assigned H III-323 (with a question mark) to NGC 4015, found by R.J. Mitchell at Birr Castle on 27 Apr 1854. And in his 1912 "Scientific Papers of William Herschel", Dreyer incorrectly equated H III-323 with "Theta" NGC 3993), based on Auwer's reduction.

400/500mm - 17.5" (3/19/88): fairly faint, moderately large, edge-on WSW-ENE, weak concentration. Located 2.5' S of a mag 10.5 star. Member of the NGC 3987/4005 group with NGC 3989 2.6' NE, NGC 3993 4.6' NE and NGC 3997 7.5' NE.

600/800mm - 24" (3/22/14): moderately bright, fairly large, very elongated 7:2 SW-NE, 1.5'x0.4', large bright core, irregular surface brightness. First of 4 in a string with NGC 3989 2.6' NE, NGC 3993 4.7' NE and NGC 3997 7.7' NE. A mag 10.5 star is 2.4' N.

Notes by Steve Gottlieb