Protoplasts from a nitrate reductase deficient mutant of N. tabacum 'Gratersleben' (n = 24) were fused with protoplasts from a stamenless, cytoplasmically male-sterile mutant of N. tabacum 'Burley 21' (2n = 48) containing the cytoplasm of N. suaveolens. Of 29 regenerated plants, stamen production was restored in 26 and pollen production in 22. One plant was male-sterile and two did not flower. Electrophoretic analysis of ribulose-1,5-diphosphate carboxylase (RuBPcase) showed that 19 plants contained RuBPcase of N. suaveolens type, six contained the N. tabacum type and four contained both types. Analysis of resistance to tentoxin in seedlings from 20 of the plants showed that 14 had N. suaveolens type chloroplasts, three had N. tabacum type and three contained both types. Many of the plants which produced stamens and pollen contained N. suaveolens chloroplasts, indicating that cytoplasmic male sterility is not an expression of the chloroplast genome.