A symposium paper with discussion. Biological problems arising from modern research techniques are too complex to be solved without the most powerful techniques of mathematics and engineering analysis. Compared with the usual engineering problems, however, biological problems are ill-defined and immensely complex. The cooperation of specialists from each side is required. A problem in fetal blood flow, from the work of Professor George Bekey of USC, is used as illustration of the point that first-order simulations are inadequate. A biological system seems always to have closed-loop communication lines, so that a change in one variable affects every other variable. (Presented at the Symposium on the Impact of Bioengineering on Engineering Education, sponsored by Oak Ridge Associated University, August 1966.).