A status report on the RAND-developed capability for interactive modeling of dynamic systems using the GPSS flowcharting technique on the GRAIL (Graphical Input Language) facilities. Analysts are dissatisfied with the long lead time required to translate a proposed simulation from a logical flow diagram to a detailed set of computer instructions to be keypunched. These steps can be bypassed by working at a GRAIL console, drawing on the RAND Tablet and having the symbols recognized and displayed by the character recognition program. Using the GRAIL/GPSS system increases the analyst's efficiency tenfold to a hundredfold. GRAIL capabilities not yet incorporated include shrinking, enlarging, and moving geometric figures, and monitoring on-line execution of the flow diagram. (Presented at an IBM Seminar on Operations Research in the Aerospace Industry: Models in Planning and Control, Newport Beach, April 1968.) 14 pp. Refs.