We present a brief discussion of some basic features of HIV dynamics. Within a multiple compartment framework, we model the dynamics of HIV subsequent to the application of a highly active antriretroviral therapy (HAART) considering blood and lymphatic system compartments. We show that T-cell and HIV decay rates after HAART correspond to time dependent effective coefficients which include transfer between the compartments, stressing that a main component in the evolution of viral concentration is redistribution. In our analysis the viremia decay rate appears to be mainly determined by the effective lymph node-viral decay rate rather than by the decay constant of infected T CD4 cells. We also show that in a two type T cell model with a transition from type 1 to type 2, the more active cells with a shorter life are the porgenitors of the less active ones.