The expression and secretion of recombinant human tumor necrosis factor-beta (TNF-beta lymphotoxin) was examined in seven different insect host cell lines, namely, Spodoptera frugiperda (Sf) 9-ATCC, Sf9-IXP, Sf21, Trichoplusia ni (BTI-TN-5B1-4), Mamestra brassicae (IZD-MB-0503), IPLB-HZ1075, and Antheraea moth ovarian cells. The highest yield of secreted recombinant human TNF-beta was obtained by using the Sf21 cells; the maximum protein productivity achieved was 71.7 mu g 1(-1) x 10(6) Sf21 cells. This is an increase of 100% over the yields obtained from the Sf9-ATCC cells. In addition, a new cell clone, Sf9-IXP, was derived which was larger in cell volume and had a 76% higher TNF-beta expression and secretion in comparison to the native original Sf9 cells. Sf9-ATCC cells infected with recombinant baculoviruses secreted TNF-beta at 32.1 mu g 1(-1) x 10(6) cells. The lowest productivity was seen for IPLB-HZ1075 cells which attained 7 mu g 1(-1) x 10(6) cells. There is a proportional relationship between increased protein production and the increase in cell volume and granularity. Recombinant protein expression and secretion was also shown to be influenced by the intracellular metabolic activities of the cells and it was observed that the recombinant human TNF-beta expressed and secreted by the different insect cells has the same molecular weight.