Thls paper descrlbes ELAB. a knowledge-based, exploratory design and learnlng environment for four-poles, electronic clrcults, conslsting of reslstors, capacitors and coils. Varlous kinds of four-poles may be constructed by the user and experlmented wlth. The system contalns a simulator that Is augmented by a component contalnlng knowledge about the simulation process and the appllcatlon domaln. The. system supports quantitative analysis as weil as qualitative Investlgatlon of the behavloral propertles of user deslgned four-poles by provldlng adequate simulation parameters, answerlng questlons about the appllcatlon domain. and glvlng examples and partial solutIons for problems posed by the user. The system makes heavy use of a dlrect manipulation interface and employs several types of vlsuallzatlon techniques.