Prolactin (PRL) interacts with lymphocyte‐signaling molecules and cytokines. Previous work has shown independent and synergistic effects of PRL on the generation of IL‐2‐driven anti‐tumor lymphokine activated killer (LAK) activity by peripheral blood mononuclear cells (PBMC). The potential importance of PRL as a biological immunomodifier, however, is challenged by its ability to influence normal lymphocyte mitogenesis and hence lymphoid tumor growth. Since non‐Hodgkin's lymphoma (NHL) cell lines were efficiently killed by LAK generated with native (n) or recombinant (r) human PRL combined with low, per se ineffective doses of IL‐2, we have addressed here the question of whether PRL acts as a growth factor for LAK targets. NHL cells were analyzed for: 1. expression of the PRL receptor (PRL‐R); 2. responsiveness to nPRL or rPRL; 3. constitutive expression and release of PRL; 4. existence of a PRL autocrine loop. PRL‐R, defined by multiple antibodies, was detected in 3 of 12 NHL cell lines. However, nPRL or rPRL, in a wide range of concentrations (0.75–50 ng/ml), were not mitogenic for growth‐arrested, PRL‐R positive NHL cell lines. PRL mRNA was detected by RT‐PCR in 10 of the 12 cell lines examined with a higher frequency among AIDS‐related NHL cell lines. PRL protein in the immunoprecipitate of ³⁵S‐methionine‐labeled cell lysates and supernatants paralleled mRNA expression, and Western blotting analysis showed the presence of the pituitary/lymphocyte non‐glycosylated (23.5 kDa) and glycosylated (25 kDa) isoforms. Experiments with blocking antibodies showed the independence from endogenous PRL for NHL cell growth. Int. J. Cancer 85:124–130, 2000. © 2000 Wiley‐Liss, Inc.