An experiment was conducted to study the influence of dietary total phosphorus (TP) level and source on the performance of two strains of S. C. White Leghorn hens for two consecutive production years (26-68 and 76-116 weeks of age, respectively). Diet 1 contained .4% TP; diets 2, 3 and 4 contained .5, .6 and .7% TP from dicalcium phosphate (DCP); diets 5 and 6; and 7 and 8 contained .5 and .6% TP from each of two raw rock phosphates (RRP-1, RRP-2), respectively. Diet 1 was statistically inferior to the average of all supplemental diets relative to feed consumption rate and egg weight during the first year, and relative to egg weight, feed consumption rate, egg production and bone ash values during the second year. The lowest TP level allowed greater shell quality or strength during the first year. Increasing TP from DCP resulted in increased feed consumption, improved feed conversion ratio, greater Haugh units, and lower shell quality during the first year. Hens receiving RRP diets responded differently during the first and second years. DCP was superior to the RRP's as to supporting egg weight during the second year, and superior in feed conversion during both years. Strain A produced larger eggs than strain B. A force molting study was conducted with hens surviving the first year. Birds were force molted by either feeding a low-sodium diet or by water and feed restrictions. The low-sodium group ceased production in about 30 days, lost 8.7% of their pre-molt body weight, decreased egg production by 70%. The second group ceased egg laying within 11 to 12 days, lost 17% of their pre-molt body weight and decreased egg production by 93%. No differences were observed between treatment groups in all response criteria studied during 10 subsequent 28-day periods. A third study was conducted to determine the effect of dietary phosphorus levels and feeding regimen on layer performance. Continuous feeding of .40, .45, .50, .55 or .60% TP from 20 to 68 weeks of age was compared with feeding decremental TP levels of either .60, .55, .50 and .45%, or .55, .50, .45, and .40% for intervals of 20-32, 33-44, 45-56 and 57-68 weeks of age, respectively. TP levels and regimen did not affect cumulative egg production, specific gravity and egg weight, but significantly affected egg specific gravity at 56 and 68 weeks, bone ash and tibia breaking strength at 44, 56 and 68 weeks of age. Phase feeding regimens significantly enhanced egg specific gravity.