LPS-activated [³⁵S]methionine-labeled macrophages were harvested immediately (Pulse) or treated with 2 mM ATP (where indicated) for 15 min and chased for 3 h in the absence or presence of 10 μM ethacrynic acid. Cell and media samples were harvested separately, each was divided into two equal fractions, and IL-1α and IL-1β were recovered by immunoprecipitation. The resulting immunoprecipitates were separated by SDS-PAGE, and radioactivity associated with individual species was determined. The quantity of radioactivity recovered intracellularly in association with the 35-kDa (35_I) and 28-kDa (28_I) forms and extracellularly in association with the 35-kDa (35_e), 28-kDa (28_e), and 17-kDa (17_e) forms of IL-1β are indicated; counts recovered as the 17-kDa species of IL-1β were multiplied by 2 to correct for loss due to proteolytic processing. Likewise, the quantity of radioactivity recovered intracellularly in association with the 31-kDa (31_I) form and extracellularly in association with the 31-kDa (31_e) and 17-kDa (17_e) forms of IL-1α are indicated; counts recovered as the 17-kDa IL-1α species were multiplied by 1.5 to correct for loss due to proteolytic processing. Total radioactivity (sum of all individual species) also is indicated. Each value is the average of duplicate determinations.