Somatostatin (SST) and somatostatin receptors (SSTR) are widely distributed in lymphoid tissues. Here we report on stimulatory effects of SST in Epstein-Barr virus-immortalized B lymphoblasts. By RT-PCR, we demonstrated the exclusive expression of the somatostatin receptor isoform 2A (SSTR2A) in B lymphoblasts. Addition of SST rapidly increased the cytosolic free calcium concentration, [Ca²⁺]_i, maximally by about 200 nM with an EC₅₀ of 1.3 nM, and stimulated the formation of inositol phosphates. Furthermore, SST increased binding of guanosine 5'--thio triphosphate by 50% above basal. These effects were partly inhibited by pertussis toxin (PTX), which indicates the involvement of PTX-sensitive G proteins. We provide further evidence that G₁₆, a PTX-insensitive G protein confined to lympho-hematopoietic cells, is involved in the otherwise unusual coupling of SSTR2A to phospholipase C activation. In addition, SST activated extracellular regulated kinases and induced a 3.5-fold stimulation of DNA synthesis and a 4.4-fold stimulation of B lymphoblast proliferation which was accompanied by an enhanced immunoglobulin formation. Thus, SST exerts a growth factor-like activity on human B lymphoblasts.