These definitions have been complicated by results that show Rab7-positive vesicles can carry out lysosomal functions including the degradation of extracellular cargo. Similarly, LAMP1 has been associated with late endosomes or pre-lysosomes. Lacking from previous work is an examination of Rab7 and LAMP1 simultaneously. Using confocal fluorescence microscopy to image Rab7 and LAMP1, we find that the majority of endo-lysosomal vesicles are positive for both Rab7 and LAMP1. This high percentage of Rab7/LAMP1-vesicles was not unique to the BS-C-1 cells, but was also observed in HeLa cells. To probe the function of these three distinct populations of endo-lysosomal vesicles we measured the transport of dextran, a fluid-phase cargo, over relatively long time scales. Of specific interest was whether the Rab7/LAMP1-vesicles were intermediate, and do not retain cargo, or terminal, with the accumulation of cargo. After a 30 min incubation, dextran was found in all populations of vesicles with 55% of Rab7/LAMP1- vesicles containing dextran. At longer times, the percentage of LAMP1- and Rab7/LAMP1-vesicles containing dextran increases with.90% of Rab7/LAMP1-vesicles containing dextran after a 1 hr pulse and 4 hr chase. LAMP1-vesicles show a similar increase in the percentage containing dextran. In comparison, the percentage of Rab7-vesicles containing dextran decreases from incubation. Terminal vesicles, in the absence of degradation, show an accumulation of cargo as a function of time as observed for LAMP1-vesicles. Interestingly, Rab7/LAMP1-vesicles behaved similarly to LAMP1-vesicles with an increase in dextran over time. In this sense, the Rab7/LAMP1-vesicle is best described as a terminal vesicle rather than an intermediate between late endosomes and lysosomes. The decrease of dextran in Rab7- vesicles as a function of time can be formally attributed degradation of dextran or the fluorophore, recycling to the plasma membrane, or transport to another endocytic vesicle. The use of dextran as endocytic cargo limits these options as it is not degraded by the cell. As recycling is not expected to occur from the late endosome and the fluorophore is stable in the other vesicles, it is most likely that dextran is transported from Rab7 vesicles to LAMP1 and Rab7/LAMP1-vesicles although that is not measured directly in these experiments. We focused on two possible mechanisms to understand the observed accumulation of dextran in LAMP1 and Rab7/LAMP1-vesicles. The first approach was to characterize each vesicle population in terms of the presence or absence of M6PR. M6PR, which is rapidly recycled from the lysosome, is commonly used to differentiate endosomes and lysosomes with lysosomes defined as M6PR-negative. We hypothesized that LAMP1- and Rab7/LAMP1-vesicles would show minimal colocalization with M6PR, as expected for lysosomes. Previous research using cryo-electron microscopy to follow the transport of cationized ferritin and horse radish peroxidase showed that LAMP -positive/M6PR-negative vesicles were terminal vesicles. Instead, we find that Rab7/LAMP1-vesicles are terminal vesicles for the transport of dextran and are also GDC-0199 Bcl-2 inhibitor M6PR-positive.