## Facts

- Donna Castillo, about seven weeks pregnant in November 1989, alleged she was drenched by drifting spray from a tractor applying DuPont’s fungicide Benlate at a nearby “u-pick” farm operated by Pine Island Farms.
- Benlate’s active ingredient is benomyl; the Castillos alleged benomyl entered Donna’s bloodstream and caused their child’s microphthalmia (severely underdeveloped eyes).
- The Castillos sued DuPont and Pine Island for negligence and products liability, alleging prenatal exposure to Benlate/benomyl caused the birth defect.
- The Castillos offered causation testimony from Dr. Charles Vyvyan Howard, a pathologist/toxicologist, who opined that fetal exposure to benomyl at about 20 parts per billion in maternal blood would cause microphthalmia in humans.
- Dr. Howard’s opinion relied on animal toxicology (rat gavage) studies, laboratory work on human and rat cells, dermal and genetic testing, and differential diagnosis; he discounted epidemiological studies as unhelpful for the causation question presented.
- The trial court denied defendants’ Frye motion in limine, admitted Dr. Howard’s testimony, and a jury found DuPont strictly liable and both DuPont and Pine Island negligent.
- The Third District Court of Appeal reversed, holding Dr. Howard’s testimony inadmissible under Frye for lack of proof that his causation methodology was generally accepted.
- The Florida Supreme Court accepted review based on conflict with a prior decision addressing Frye’s application to expert testimony.

## Issues

1. Whether the plaintiffs’ causation opinion evidence constituted new or novel scientific evidence subject to Frye.
2. If Frye applied, whether the expert’s methodology (including extrapolation from animal/in vitro data and differential diagnosis) was generally accepted in the relevant scientific community.
3. Whether the district court erred by treating disagreement with the expert’s conclusions (including an asserted exposure threshold) as a Frye admissibility defect.

## Decision

- The Florida Supreme Court quashed the district court’s decision.
- The Court held the plaintiffs’ expert testimony was admissible under Frye.
- The Court concluded the district court misapplied Frye by focusing on contested conclusions rather than the general acceptance of the underlying scientific methods.
- The Court reinstated the trial court’s admissibility ruling, leaving disputes over causation strength for the jury to weigh.

## Legal Principles

- Frye applies in Florida only to new or novel scientific evidence; it is not a general test for all expert opinions.
- Frye asks whether the underlying scientific principle or methodology is generally accepted in the relevant field, not whether the expert’s ultimate conclusion is generally accepted.
- Traditional scientific and medical tools (including animal toxicology, laboratory studies, and differential diagnosis) may be admissible when used in a causation analysis; opposing views ordinarily go to weight, not admissibility.
- “Pure opinion” testimony grounded in an expert’s training and experience, rather than a novel scientific technique, is not subject to Frye.

## Conclusion

The Florida Supreme Court held that the plaintiffs’ toxic-tort causation expert could testify because the methods employed were generally accepted and Frye does not authorize exclusion simply because the expert’s causal inference and proposed exposure threshold are disputed.


Castillo v. E.I. Du Pont De Nemours & Co., 854 So. 2d 1264 (Fla. 2003)