Relations between pairwise correlations and the coefficient of multiple determination in regression analysis are considered. The conditions for the occurrence of enhance-synergism and suppression effects when multiple determination becomes bigger than the total of squared correlations of the dependent variable with the regressors are discussed. It is shown that such effects can occur just for stochastic relations among the variables that have non-transitive signs of pairwise correlations. Consideration of these problems facilitates better understanding the properties of regression.