The amine salts of 2,4-D and picloram were applied to the Florida species of mangroves: red mangrove (Rhizophora mangle), white mangrove (Laguncularia racemosa) and black mangrove (Avicennia germinans). Treatments were to soil or water, by aerial spray and to single leaves as droplets. The effects on radiochloride uptake and on localization of radiocarbon-labelled picloram after leaf application were studied in red mangrove. Spray applications of 6.3 - 12.2 kg/ha of commercial mixture to the canopy of a mixed-species forest caused partial defoliation within three weeks. Within 16 months it killed all of the white, 78 - 100% of the mature red, but none of the mature black mangroves. Radiocarbon-labelled picloram concentrated in dormant buds of red mangrove and it is concluded that the tree is killed by the mixture because of its effects on them.