Approximately 1/2 of the macronucleoplasm of wild-type cells of Paramecium tetraurelia was transplanted into d4-84 mutant recipient homozygous for mutations nd3a (non-discharging trichocysts) and ts401 (temperature sensitive). After injection, 30% of surviving cells shifted from mutant to wild-type phenotype. Among the remaining cell lines 29% were unable to eject any trichocysts, and 41% discharged less than 10 of them per cell, when tested with picric acid. Observations were made through two successive vegetative fissions. These results showed that 30% of d4-84 cells contained foreign gene responsible for trichocyst discharge and produced cell lines of the wild-type phenotype, in which the expression as well as replication of this gene appeared normal.