Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The essential oil isolated by hydrodistillation from unripe fruits of Myrcia laruotteana Camb. (Myrtaceae) was analyzed by GC and CG/MS. Forty-four components were identified, representing around 83% of total oil. The major components were a-bisabolol (23.6%) and a-bisabolol oxide B (11.5%). The cytotoxicity of the oil and of a fraction rich in a-bisabolol was tested in vitro against U251 (glioma), UACC-62 (melanoma), MCF-7 (breast), NC1-ADR/RES (ovarian-resistant), 786.0 (kidney), NCI-H460 (lung), PC-3 (prostate), OVCAR-3 (ovarian), HT-29 (colon) and K562 (leukemia) human cancer cells and against VERO (no cancer cell). The oil exhibited antiproliferative activity against all cell lines (TGI < 100 mu g/mL), with exception of NCI-H460 cell line (TGI > 125 mu g/mL). The highest activity of the oil was observed against U251 (TGI 20.46 mu g/mL), 786.0 (TGI 20.74 mu g/mL), UACC-62 (TGI 26.98 mu g/mL) and PC-3 (TGI 27.63 mu g/mL) cell lines. The fraction rich in alpha-bisabol showed a similar activity profile. It was most active against OVCAR-3 (TGI 8.58 mu g/mL) and 786.0 (TGI 8.74 mu g/mL).235SI710Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)