Two-line rice hybrids were found to be more heterotic than three-line hybrids. Constraints of the three-line system can also be avoided in the two-line system. Any rice variety can be used as a pollen parent in the two-line system irrespective of the presence of a restorer gene. The two-line system also offers the advantage of easy seed production. For photoperiod-sensitive genic male sterility (PGMS) vs thermosensitive genic male sterility (TGMS), the TGMS system is more useful for the weather conditions that prevail in southern India. We therefore screened some diverse genotypes to identify potential lines. Staggered sowings and plantings were done during the 1995-96 wet and dry seasons. We carried out pollen studies on these lines and also re- corded spikelet fertility. Data on pollen sterility were correlated with minimum, maximum, and daily mean temperatures during the critical period of sensitivity of the lines, that is, 10 d from the third day after panicle initiation.