On the Jornada Experimental Range more total forage is obtained by grazing tobosa range during summer and reserving black grama ranges for use during the nongrowing season. Black grama range so deferred for 20 years now supports eight times as much black grama and only 1/9 as much snakeweed as adjacent comparable range grazed year long. Forage production was also maintained at a higher level under seasonal grazing. On the more uniform range types of the Santa Rita Experimental Range, where types that are adapted to grazing in only one season are not marked, advantages of rotation grazing are not so clearly evident. However, observations and data accumulated along fence lines and in small traps that have been grazed seasonally indicate that rest from grazing is beneficial at any time and that: (a) the forage composition is improved, (b) the yield of forage is higher, (c) recuperation from drought faster and (d) green forage is available later in the fall and earlier in the spring. Quantitative measurement and economic justification of rotational vs. year-long grazing must depend on results of tests now being planned.