The question arose whether Dunaliella acidophila is not strictly autotrophic but rather is auxotrophic. A still unknown partner microorganism could be supplying it with growth factors (e.g. vitamins). Using 14C-labelled vitamins as tracers, it was tested whether this alga can take-up vitamins when introduced in the medium. Data gathered suggest the presence of uptake mechanisms for biotin, folic acid and pantothenic acid. The calculated KM values are in the micromolar concentrations. The permeability coefficient (Ps) of the D. acidophila plasmalemma for the vitamins tested ranged from 1.5 - 5.7 x 10-11 ms-1.