Two different parallelization strategies of the discrete ordinates met
hod (DOM) are described and implemented in a distributed-memory comput
er. In the angular decomposition (ADP), each processor performs the ca
lculations for the whole domain but deals only with a few directions,
while in the spatial domain decomposition (DDP) each processor treats
all the directions but only for a subdomain. In the ADP the number of
iterations is independent of the number of processors, contrary to the
DDP, and higher efficiencies are obtained. The influence of the order
of quadrature, grid size, and absorption coefficient of the medium is
also investigated.