The glass Petri dish has served as a standard culture vessel for the maintenance of a variety of cell strains and tissue explants "in vitro". Monolayer cultures have been maintained on the inside bottom of the dish overlayed by a liquid nutrient medium. Observation of the growing cultures usually requires an inverted microscope and a marked sacrifice in optical resolution. The modified platitic culture dish comprises a 60 mm. dish bottom with a Petri style lid that has a recessed area 40 mm in diameter. The optical working distance from the top of the lid to the inside bottom of the dish (cell surface) is 2.6 mm. This feature enables one to study individual cells of the monolayer by using an ordinary light microscope with or without phase contrast optics (10X and 20X objectives).-. When making observations with an inverted microscope, the recessed lid permits the phase condenser to be focused on the cell surface thereby producing much better definition of cell structure at higher magnifications (40X objective). All of these optical procedures can be carried out with the recessed lid in place thereby decreasing the chances of contamination. This dish is helpful where rapid screening of large numbers of cultures is necessary or where inverted microscopes are not readily available.