It has not been possible to demonstrate an increase in oviposition rate inTetranychus urticae Koch and T. telarius (L.) owing to DDT treatment. Treatments included direct application, holding on treated bean leaves, rearing on bean plants inserted in water containing DDT or combinations of such treatments. It was not possible to confirm a report that daughters of treated mites produced more eggs than did the parent females. A definite harmful effect is evidenced by early mortality, lowered oviposition rate, and restlessness. The harmful effect is intensified by high temperature.