In this paper are studied five groups of experiments, comprising 44 annual results, in which topping at different phases of cotton plant development are compared with untopping. The experiments were carried out from 1930-31 to 1941-42, at several places of the State of São Paulo. On average, no increase in yield was detected when the tip of the main stem, only, was cutt off. However, the yield may be slightly depressed when this operation is done at an early stage of the flowering period or when the tips of the monopodia! branches are cut off too, at the medium or final stage of that period. No effect was observed on earliness, lint-percentage, lint-length, lint-index, seed-index, or boll weight. Such results agree with those found by nearly all experimenters at other cotton regions of the world. In final conclusion, the authors do not recommend topping, not only to save expense, but also, to avoid possible reduction in yield, caused directly by the practice, or indirectly, by its detrimental effect on the execution of other practices, which are really useful.