Ongoing quality control is necessary as part of the maintenance and improvement of a successful human in vitro fertilization (IVF) program. Using a mouse quality-control culture system, several instrument preparation protocols were reevaluated to determine their efficiency in the control or elimination of potential toxicity. Dilute concentrations of urine and endometrial fluid were also tested. Medium rinsed through laparoscope and aspiration needles failed to support embryo development. This effect was reversed in needles that were pretreated with rinses of Dulbecco's phosphate-buffered saline. Endometrial fluid demonstrated no obvious toxic effect, but urine-exposed embryos arrested in the two-cell state. The importance of periodic evaluation of materials and their pretreatment before use in in vitro fertilization of human oocytes is essential to ensure control of potentially toxic substances.