The four-body calculations for&Lgr;4Heand&Lgr;4Hwith high accuracy have been performed in the framework of the variational method with Jacobian-coordinate Gaussian-basis functions. All the rearrangement channel of bothNNN&Lgr;andNNN&Sgr;are explicitly taken into account for the first time using realisticNNandYNinteractions. The important role of&Lgr;−&Sgr;conversion and the amount of the virtual &Sgr;-component in&Lgr;4Heand&Lgr;4Hare discussed. ©2001 American Institute of Physics.