BACKGROUND:Blackberry fruits have recently gained attention because of their considerable amounts of polyphenols. OBJECTIVE:The aim of this study is to compare the physicochemical composition and contents of the main polyphenolic compounds of nine tropical highland blackberry genotypes grown in Costa Rica, and to evaluate the effect of environmental conditions and farming practices on physicochemical composition of fruits of 'Wine red thorn', which is the most widely grown blackberry genotype in Costa Rica. METHODS: Nine blackberry genotypes were harvested at fully ripe stage. Environmental conditions (geographic location and harvest season) and farming practices (organic and conventional techniques) were evaluated to determine their effects on physicochemical composition and polyphenolic compounds of 'Wine red thorn' blackberries. Anthocyanins and ellagitannins contents were determined by HPLC-DAD. RESULTS:The tropical highland blackberries contained appreciable levels of polyphenols. Anthocyanin content ranged from 2.9±0.1 to 12±1¿g cyanidin-3-glucoside equivalents/kg dry weight (DW); ellagitannin content ranged from 9.3±0.8 to 47±3¿g ellagic acid equivalents/kg DW. The influence of environmental conditions and farming practices on physicochemical characteristics of 'Wine red thorn' blackberries was significant (p¿<¿0.05). Blackberries harvested during the dry season had higher contents of sugars and anthocyanins than blackberries harvested during the rainy season. Organic blackberries had higher levels of ellagitannins than conventionally grown fruits. CONCLUSIONS:These data prove that Costa Rican blackberries are a good source of polyphenolic compounds, especially ellagitannins. Environmental and farming conditions can be exploited to obtain high quality blackberry fruits.