abstract the objective of the present work was to determine the effects of colored shading on the density of glandular and tectorial trichomes, and on the yield, productivity and composition of the essential oil of ocimum selloi benth. plants were cultivated for 90 days under full sunlight or under chromatinet 50% red or blue netting. the highest density of glandular trichomes was observed in plants that had received full sunlight. none of the light treatments ailtered the yield of oil, although productivity was higher in plants grown under full sunlight by virtue of the greater leaf biomass that accumulated under such conditions. the compositions of the oils varied according to the quality of light. although the qualitative profiles of the oils of plants grown under full sunlight or red shading were similar, that obtained from plants grown under blue shading presented a larger number of constituents. the highest level of methyl chavicol (93.2%), the major component of the oil, was observed in plants grown under full sunlight.