Erythrina crista-galli L. (Leguminosae) is the most common species of Erythrina in Argentina and was introduced into Indian gardens as an ornamental plant. Its seeds and leaves have already been studied, but its flowers have not been investigated. This paper reports the results of the studies of E. crista-galli flowers, which led to the characterization of two new alkaloids, 11β-methoxyerythraline-N-oxide [1] and 11-methoxyerythratine [2]. The dry, powdered flowers were exhaustively extracted with petroleum ether (60-80°C), and the residue was extracted with MeOH and processed to afford a free alkaloid fraction and a liberated fraction (obtained by acidic hydrolysis of any alkaloid glycosides present after removal of the free alkaloids). Both fractions were derivatized to form trimethylsilyl ethers prior to GC and combined GC/MS. GC and GC/MS examination of the petroleum ether fraction and the MeOH-soluble free alkaloid fraction showed the presence of 11β-methoxyerythraline (44%), erythrinine (33%), erythraline (12%), 8-oxoerythrinine (5%), 11-methoxyerythratine (4%), and traces of erysodine/erysovine. The liberated fraction indicated the presence of erysopine only. The petroleum ether fraction and MeOH-soluble free alkaloid fraction were identical in their TLC behavior; they were combined and chromatographed over neutral alumina to afford 11β-methoxyerythraline, erythraline, erythrinine, 8-oxoerythrinine, 11β-methoxyerythraline-N-oxide [1], and 11-methoxyerythratine [2] on the basis of their spectral characteristics. Structural assignments were achieved by ¹H-NMR spectroscopy (360 MHz). For 11β-methoxyerythraline-N-oxide, the 4-H resonance appeared at high field (δ 2.08), whereas the 4-Ha was shifted downfield (δ 3.09); the 8-H (δ 5.09, 4.71) and 10-H (δ 4.71, 3.91) resonances were about 0.7 to 1 ppm downfield compared to the parent compound, and the 11-H proton also resonated downfield (0.3 ppm). Its EI-MS showed major peaks at m/z 343 (M⁺, 2%), 327 (M⁺-16, 44%), 312 (M⁺-31, 21%), 296 (M⁺-47, base peak), 295 (M⁺-48, 94%), 294 (M⁺-49, 68%), and 280 (46%). The presence of a (M⁺-16) peak identified it as 11β-methoxyerythraline-N-oxide, and its identity was confirmed by treating 11β-methoxyerythraline with m-chloroperbenzoic acid (the resulting N-oxide was identical to the natural product). Earlier, erysotrine-N-oxide and erythrartine-N-oxide had been isolated from Erythrina mulungu flowers, and those authors noted these N-oxides are natural products rather than artifacts. The ¹H-NMR spectrum of 11-methoxyerythratine gave signals at δ 6.64 (s, 14-H or 17-H), 6.47 (s, 1H, 17-H or 14-H), 5.87 and 5.84 (2H, -OCH₂O-), 5.75 (1H, 1-H), 4.53 (t, J=4.6 Hz, 1H, 11-H), 4.31 (1H, 2-H), 3.59 (m, 1H, 3-H), 3.40 (s, 3H, 11-OCH₃), 3.36 (s, 3H, 3-OCH₃), 2.95 (m, 1H, 8-Ha), 2.60 (m, 1H, 8-He), and 1.77 (t, J=11.5 Hz, 1H, 4-Ha). The EI-MS of its trimethylsilyl derivative exhibited peaks at m/z 417 (M⁺, base peak), 329 (M⁺-88, 40%), 328 (M⁺-89, 52%), and 73 (94%). The molecular ion corresponds to a mono-hydroxylated alkaloid (molecular weight 345), and the fragment ions at m/z 328 and 329 correspond to the loss of the trimethylsilyl ether moiety, identifying it as 11-methoxyerythratine [2].