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The variable star HD 26337 = EI Eri is a chromospherically active G5 IV single-lined spectroscopic binary with a period of 1.94722 days. It has moderate strength Ca II H and K emission and strong ultraviolet emission features, while Hα is a weak absorption feature that is variable in strength. The inclination of the system is 46°±12°, and the unseen secondary is most likely a late K or early M dwarf. The v sin i of the primary is 50±3 km s-1, resulting in a minimum radius of 1.9±0.1 R_sun;. A mass ratio of M1/M2 ≥ 2.6 and a mass for the primary of at least 1.4 M_sun; is found. HD 26337 has a moderate lithium abundance log n(Li) = 1.75 - 2.0. It is suggested that many chromospherically active stars may still have moderate lithium abundances because they have evolved from late A or early F type main-sequence stars.