The few opossums caught in summer were thin and appeared to be suffering from infestations of ectoparasites, especially chiggers (_Eutrombicula alfreddugesi_) and ticks (_Dermacentor variabilis_). Those trapped in October and November were mostly fat and in good condition. For individuals caught at different seasons, maximum weights were generally recorded in these two months. The maximum weight record of the study was one of an adult male weighing 5000 grams on December 23, 1950. The weight records of this individual were more complete than most and are recorded below to illustrate seasonal trends for adults. May 10, 1950, 1925 grams; May 14, 1830 grams; May 17, 1940 grams; November 5, 4540 grams; November 28, 4540 grams; December 23, 5000 grams; February 18, 1951, 3300 grams; March 6, 3080 grams; March 28, 3080 grams; May 28, 3080 grams; June 18, 2620 grams. Of opossums that were trapped alive, the weight ranged from the maximum of 5000 grams to a minimum of 126 grams. The maximum in males was higher than in females. In fall, three rather poorly defined age-size groups were discernible in each sex: adults more than a year old and including all the largest individuals; large young born late the preceding winter and approaching small adult size; smaller young born in early summer and still less than half-grown. After November, young cease to gain, or gain slowly and irregularly through the winter and spring and adults tend to decline in weight, as food becomes scarce and frequent fasting is enforced by cold or stormy weather. The smaller young probably are subject to drastic reduction in numbers as a result, directly or indirectly, of severe winter weather. Many of these smaller young, weighing considerably less than 1000 grams, did not survive overnight when caught in live-traps in cool autumn weather, whereas adults and well-grown young generally survived exposure even for several successive nights in various extremes of weather conditions. BREEDING SEASON