Single crystals of Ln(Cu,Al)₁₂ and Ln(Cu,Ga)₁₂ compounds (Ln = Y, Ce–Nd, Sm, Gd–Ho, and Yb for Al and Ln = Y, Gd–Er, Yb for Ga) have been grown by flux-growth methods and characterized by means of single-crystal x-ray diffraction, complemented with microprobe analysis, magnetic susceptibility, resistivity and heat capacity measurements. Ln(Cu,Ga)₁₂ and Ln(Cu,Al)₁₂ of the ThMn₁₂ structure type crystallize in the tetragonal I4/mmm space group with lattice parameters a~8.59 Å and c~5.15 Å and a~8.75 Å and c~5.13 Å for Ga and Al containing compounds, respectively. For aluminium containing compounds, magnetic susceptibility data show Curie–Weiss paramagnetism in the Ce and Pr analogues down to 50 K with no magnetic ordering down to 3 K, whereas the Yb analogue shows a temperature-independent Pauli paramagnetism. Sm(Cu,Al)₁₂ orders antiferromagnetically at T_N~5 K and interestingly exhibits Curie–Weiss behaviour down to 10 K with no Van Vleck contribution to the susceptibility. Specific heat data show that Ce(Cu,Al)₁₂ is a heavy fermion antiferromagnet with T_N~2 K and with an electronic specific heat coefficient γ₀ as large as 390 mJ K² mol⁻¹. In addition, this is the first report of Pr(Cu,Al)₁₂ and Sm(Cu,Al)₁₂ showing an enhanced mass (~80 and 120 mJ K² mol⁻¹). For Ga containing analogues, magnetic susceptibility data also show the expected Curie–Weiss behaviour from Gd to Er, with the Yb analogue being once again a Pauli paramagnet. The antiferromagnetic transition temperatures range over 12.5, 13.5, 6.7, and 3.4 K for Gd, Tb, Dy, and Er. Metallic behaviour is observed down to 3 K for all Ga and Al analogues. A large positive magnetoresistance up to 150% at 9 T is also observed for Dy(Cu,Ga)₁₂. The structure, magnetic, and transport properties of these compounds will be discussed.