an agricultural drainage experiment with the tile drains installed at lateral spacings of 12. 5, 25 and 50 m and drain depth of 1. 2 and 1. 5 m was initiated in egypt in 1976 to examine long-term effects of drainage on crop production. the experimental fields were planted to cotton, clover, rice and wheat in rotation data from the three completed cropping cycles indicated that yields of all crops improved significantly after installation of subsurface drainage systems. the yield increases of field drained with 12. 5 and 25 m lateral spacings were, respectively, 39 and 16 higher than that with 50 m lateral spacing. drain depths of 1. 2 m and 1. 5 m did not significantly affect the crop production. by installing drainage systems, net profits of crop production may increase 5 to 8 times. lateral spacings and drain depths, however, did not appear to significantly affect the financial return. additional study results are discussed. (edited author abstract) 12 refs