We show that if R is an exchange ring with primitive factors artinian then K 1 ( R ) ≅ U ( R ) / V ( R ) , where U ( R ) is the group of units of R and V ( R ) is the subgroup generated by { ( 1 + a b ) ( 1 + b a ) − 1 | a , b ∈ R with 1 + a b ∈ U ( R ) } . As a corollary, K 1 ( R ) is the abelianized group of units of R if 1 / 2 ∈ R .