Experiments conducted on seedling age and different water depths revealed that short-duration, 7-day flooding o f 3- week-old seedling was effective in assessing elongation potential in deepwater rice varieties. Water depths o f 90-100 cm were sufficient to express elongating ability and 3-week-old seedlings gave better contrast between elongating modern varieties and non-elongating modern varieties. Maximum internode length was under short-day-length conditions while shortest internodes were obtained in the long day treatment. Internode elongation may be due only to the signal effect o f day length or the shading effect on assimilation. Further experiments should be conducted to confirm these findings.