BACKGROUND: Synthetic organic polymer flocculants can be highly effective at clarifying suspensions, but these substances may also have negative environmental and health effects. Relatively few studies have been done using biobased flocculants, which aremore environment friendly. Hemoglobin (Hb) haspreviously been demonstrated to be a promising flocculant of kaolin and lignin suspensions. This study examines themethylation of Hb side chain carboxyl groups for the purpose of improving its flocculation performance at near-neutral pH. RESULTS: Potentiometric titration of methylated Hb (MeHb) showed an approximately 28% degree of methylation when the Hb was suspended in methanol with 0.8 mol L-1 HCl for 48 h. Under some conditions, MeHb clarified suspensions of kaolin at one-quarter the dose thatwas required forHb. Furthermore, MeHb exhibited flocculant activity over a widepHrange, compared withHb. The percentage of original turbidity removedwas37% forHbwhile60% of the original turbiditywas removed forMeHb at near-neutral pH (pH = 6.8). CONCLUSIONS: Very small doses ofmethylated hemoglobin (MeHb) rapidly clarify suspensions of kaolin. The potential of MeHb as a biobased flocculant for the clarification of water for industrial or municipal use was demonstrated. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.