Cell suspension cultures of white clover (Trifolium repens L. ‘Regal Ladino’) were treated with 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], 2,4,5-TP [2-(2,4,5-trichlorophenoxy) propionic acid], and 2,4,5-TB [4-(2,4,5-trichlorophenoxy)butyric acid]. Cell population densities were monitored throughout the treatment period and herbicide remaining in the cells and culture medium was extracted and quantified at the termination of the treatment. Herbicide tolerance increased in cell populations which were conditioned by pretreatment with 2,4-DB and 2,4,5-T. However, 2,4-DB was rapidly degraded by all cell populations regardless of pretreatment. White clover cell suspension cultures treated with 2,4-D, 2,4-DB, 2,4,5-T, 2,4,5-TP and 2,4,5-TB metabolized the homologs, according to the following sequence: butyric acidåpropionic acidåacetic acid homologs. There was no difference in the rate of degradation of similar homologs of the 2,4-dichloro- and 2,4,5-trichloro- analogs.