SUMMARYThe effects of five different environments, outside under natural conditions, glasshouse, Polythene enclosures (two designs), and muslin shades, upon seed development and seed quality in four varieties of forage grasses were investigated in two years. In 1972 pollen release occurred first in the Polythene enclosure and the highest pollen counts were obtained from this treatment and under glasshouse conditions. Plants in which seed development occurred in the glasshouse had the highest floret fertility, 1000 seed weight and seed weight per inflorescence, while those grown under Polythene gave low values for all these characters. Plants in which seed development occurred under muslin shades, where light intensity was reduced by half, gave seed yields equal to those grown in full day‐light. In 1973 the germination rate was highest in seeds produced under Polythene and lowest in those produced under outside conditions. The dry weights of seedlings from the outside treatment were lower than those from the glasshouse and Polythene enclosures in four of the five experiments. It is suggested that isolation methods for the production of small seed lots should be standardized, and that glass isolation chambers are the most efficient method of producing small seed lots for plant breeding and agronomic investigations.