The effects of temperature and relative humidity on stigma receptivity in a cytoplasmic male sterile wheat line were estimated by measuring per cent seed set on plants raised in controlled environments in the phytotron at Canberra. Three levels of temperature (26¦C day : 21¦C night, 18¦C : 13¦C, 10¦C : 5¦C) and two levels of humidity (75-90 per cent, 40-60 per cent) were combined with four times of pollination (1, 3, 5, and 7 days after flowering) in a factorial design. Stigma receptivity was maintained at a high level under moderate temperature and low humidity conditions. Mean seed set on plants pollinated seven days after flowering was 41.2 per cent at the moderate temperature compared with 0.5 per cent at the high temperature, and 43.2 per cent at the low humidity compared with 7.1 per cent at the high humidity. The effects of temperature and humidity were additive. With a moderate temperature-low humidity combination seed set was as high as 77.4 per cent on plants pollinated seven days after flowering. With the combination of high temperature and high humidity seed set decreased to 0.4 per cent on plants pollinated five days after flowering.