Rab GTPases reside in specific intracellular compartments and are key regulators of vesicular transport. To facilitate studies of the mechanism of lysosomal integral membrane protein (LAMP-1) transport, cDNAs for human Rab7 and Rab9 were isolated, and their nucleotide sequences were determined. During isolation and characterization of these cDNAs a Rab9 pseudogene was identified. The sequences are highly homologous to other mammalian Rab proteins and also share homology with proteins of the Rab GTPase family. Rab7 and the Rab9 pseudogene were mapped to chromosomes 3 and 5, respectively, by amplification of their sequences from human monochromosomal somatic cell hybrids. In addition, preliminary studies using antisense expression indicate that down-regulation of either Rab7 or Rab9 proteins induces severe cell vacuolation that resembles the phenotype seen in fibroblasts from patients with Chediak-Higashi syndrome.