The soybean aphid, Aphis glycines , is an introduced pest of soybeans, Glycine max (L.) Merr. in North America . Since 2000 when the soybean aphid was first detected in the US , studies of this insect and possible control methods have been initiated. A. glycines populations increase quickly, spread very rapidly, cause severe damage and may reduce yields by 50%. A. glycines also vectors viral diseases such as soybean mosaic virus. We studied soybean resistance to the soybean aphid on more than 200 entries, and few entries showed some levels of antibiosis and antixenosis as categories of resistance to the soybean aphid. These entries, along with the susceptible checks KS4202 and 93B15, were selected for studying the chlorophyll losses caused by the soybean aphid in a true no-choice test, in which aphids were confined in double-sided sticky cages placed to the upper side of leaves. We developed a protocol using the susceptible check KS4202. Zero, Five, 10, 20, 30 and 40 aphids were confined in the cages and after four, seven and 10 days of infestation the chlorophyll content was measured using the SPAD chlorophyll meter. After several experiments using the susceptible check KS4202, the treatments with 30 and 40 confined aphids for 10 days showed differences in chlorophyll content between infested (I) and no-infested (NI) leaves. Chlorophyll content on resistant entries was not different between I and NI leaves.