Three crystal forms were found for (rac-1-cyanoethyl)bis(2,3-butanedione dioximato)(pyrrolidine)cobalt(III). Two forms, (I) and (II), were grown from solutions of aqueous methanol and benzene-chloroform, respectively, and the third, (III), was obtained by crystalline-state racemization [Takenaka, Ohashi, Tamura, Uchida, Sasada, Ohgo & Baba (1993). Acta Cryst. B49, 272-277]. The structures of (I) and (II) have been determined. (I): [Co(C 3 H 4 N)(C 4 H 9 N)(C 4 H 7 N 2 O 2 ) 2 ], triclinic, P1, Z= 4, a=11.723 (2), b=15.658 (3), c=11.118 (2) A, α=98.71 (2), β=90.17 (4), γ=98.52 (3) o , V= 1994.2 (8) A 3 , R=0.065, wR=0.079, M r =414.4, D m =1.39, D x =1.38 Mg m -3 , μ(Mo Kα)= 0.887 mm -1 , F(000)=872, T=296 K. (II): [Co(C 3 H 4 N)(C 4 H 9 N)(C 4 H 7 N 2 O 2 ) 2 ].3/2C 6 H 6 , monoclinic, P2 1 /a, Z= 4, a=16.621 (2), b=18.803 (2), c=9.155 (1) A, β=105.03 (2), V=2763.4 (7) A 3 , R=0.085, wR=0.105, M r =531.6, D x =1.28 Mg m -3 , μ(Mo Kα)= 0.655 mm -1 , F(000)=1124, T=296 K