In the spectrophotometric determination of cobalt with 2,2'-dipyridyl ketoxime, the effects of several ions were studied. Among tre ions studied, only cupric nichelous, ferric and manganous cations interfered. The interference caused by cupric, nichelous and ferric cations was iliminated by a second extraction of the colored compound with a 2N hydrochloric acid solution. The interference, of the manganous cation, disappear when cobalt is determined in the presence of other ions.