Lamellar MnPS3, ZnPS3 and bipyridine-intercalated MnPS3 are found to include intralayer metallic monovacancies, through which positrons annihilate with a lifetime of 0.30 ns. Positrons in pyridine-intercalated FePS3 decay with a lifetime of 0.35 ns, which is explained in terms of a mean lifetime for positrons annihilating with 0.30 ns through monovacancies and those with 0.36 ns through divacancies, in a ratio of ca. I : 5. The lifetime of positrons in vacancies decreases continuously with decreasing temperature from 270 to 30 K, and no abrupt change in lifetime is found at the critical temperature for antiferromagnetic ordering.