We prove that the groups
⟨
a
,
b
;
(
a
−
1
b
l
a
b
m
)
t
⟩
\langle a,b;{({a^{ - 1}}{b^l}a{b^m})^t}\rangle
, where
l
,
m
,
t
∈
Z
l,m,t \in Z
and
t
⩾
2
t \geqslant 2
are residually finite
(
R
F
)
{(_R}F)
, thus establishing a conjecture of G. Baumslag [Bull. Amer. Math. Soc. 73 (1967), 618-620].