Thidiazuron (TDZ; N-phenyl-N-1,2,3-thiadiazol-5-ylurea) stimulates axillary bud break in some horticultural crops. We are exploring its ability to initiate bud growth in mango trees in order to manipulate vegetative and reproductive shoot initiation. Axillary buds on defoliated, decapitated shoots were treated in late October, 1989 (about two months before normal floral initiation), with 0, 125, or 1000 ppm TDZ. Although timing or percent of bud-break was unaffected by TDZ, the compound influenced growth expression. TDZ (125 ppm) produced morphologically typical panicles (mixed or purely floral), while at 1000 ppm purely floral panicles were produced which were abnormally compact (similar to panicles affected by mango malformation). Non-treated buds produced only vegetative shoots. Sprays of TDZ (25 to 200 ppm) on developing panicles produced morphological anomalies in panicles such as thickening of the central axis and secondary branches, increase in flower size, and sprouting of the most basal buds on the central axis. Effect during the vegetative flushing period will be discussed.