In this section, we present the empirical findings on the relationship between working capital management and profitability of the American manufacturing firms. We used the weighted least square model with cross section weight of five industries (health care manufacturing, industrial products manufacturing, chemical products manufacturing, energy products manufacturing, and food production). When we use the pooled data and cross sections, there may be a problem of heteroskedasticity (changing variation after short period) [2, P. 292). To counter this problem, we used the general least square with cross section weights. In this regression, the common intercept was calculated for all variables and assigned a weight.