Growth and yield of Oct.-sown Capsicum annuum, cv. Delphin, were investigated in a greenhouse under 12 day/night temperature regimes (16/15 degrees , 16/21 degrees , 20/12 degrees , 20/15 degrees , 20/18 degrees , 20/21 degrees , 24/12 degrees , 24/15 degrees , 24/18 degrees , 24/21 degrees , 28/15 degrees and 28/21 degrees C) applied during the early post-planting period (early Dec. to mid-Apr.). Fresh weight and leaf number were significantly correlated with 24-h mean temperature, but no significant effect of the day/night temperature amplitude was found. Plant height, leaf area and the leaf-area:length ratio were significantly correlated with 24-h mean temperature and with day/night temperature amplitude. The optimum 24-h mean temperature for vegetative growth was between 21 and 23 degrees . Yields of total and class 1 fruits (kg/msuperscript 2) and numbers of class 1 fruits were greatest at a 24-h mean temperature of 21-21.5 degrees . Raising the 24-h mean air temperature within the range 16.3 to 23.8 degrees significantly reduced the mean fruit weight of class 1 fruits. The day/night temperature amplitude had a significant positive effect on these variables. The effect of the day/night temperature amplitude on vegetative growth and on yield was of minor importance compared with the effect of the 24-h mean temperature. (Abstract retrieved from CAB Abstracts by CABI’s permission)