The effects of the non-planar polychlorinated biphenyl (PCB) congener 2,2',4,4'-tetrachlorobiphenyl (2,4-TCB) and of the coplanar PCB congener 3,3',4,4'-tetrachlorobiphenyl (3,4-TCB) were investigated on the catecholamine content and release from bovine adrenal chromaffin cells in culture. Each congener was tested at three concentrations (20, 50 and 100 μM) and two exposure periods (24 h and 5 days). Catecholamine release induced by K+-stimulation as well as catecholamine content of Triton X-100 treated cell cultures were examined using high-performance liquid chromatography (HPLC). 2,4-TCB showed dose- and time-dependent effects. 2,4-TCB at 100 μM reduced the K+-stimulated catecholamine release after 24 h of exposure. After 5 days of exposure, 2,4 TCB at 50 and 100 μM drastically reduced the Kt-stimulated catecholamine release. 3,4-TCB even at a concentration of 100 μM over exposure of either 24 h or 5 days had no effects on the K+-stimulated secretion. When chromaffin cells, exposed to 2,4-TCB, were lysed with 0.5% Triton X-100, a dose- and time-dependent reduction of the catecholamine content appeared. The 3,4-TCB did not reduce the catecholamine content. Conversely there seemed to be a trend towards an increase in catecholamine content. Spontaneous release of catecholamines was strongly increased by the non-planar 2,4 TCB, while the coplanar 3,4 TCB showed no effects on this parameter. Furthermore, the effects of 2,4 TCB appeared to be reversible after replacing the highest concentration (100 μM) of the TCB-solution with culture-medium at the end of the 24-h exposure. Thus, K+-stimulated catecholamine release and the catecholamine content of bovine adrenal chromaffin cells was effectively reduced by the non-planar PCB congener whereas spontaneous catecholamine release was strongly increased. The coplanar PCB congener was ineffective at the same conditions.