Prominent toxicologist Peter Dingle says claims he made a pact to write a book about his wife being cured of cancer using alternative therapies are ridiculous.

Dr Dingle was giving evidence at an inquest into the death of his wife, Penelope.

She was diagnosed with colorectal cancer in 2003, but died after deciding to be treated by a homoeopath instead of conventional medicine.

A witness had told the inquest that Mrs Dingle had undergone emergency surgery to remove a tumour.

But after the surgery, the witness said Mrs Dingle, her husband and her homoeopath had made a pact that once she was cured of cancer, he would write a book that would advance the cause of homoeopathy in Australia.

The witness testified that Mrs Dingle then said she felt foolish and stupid that she may not survive what she called a "monstrous experiment".

In his evidence today, Dr Dingle said it was ridiculous to suggest that he was going to write a book, saying his number one priority had been his wife.

Mrs Dingle's family has raised concerns that Dr Dingle misled his wife into believing that alternative therapies could cure her.

Dr Dingle testified that he wanted his wife to have surgery shortly after she was diagnosed, but she refused. He said that his wife made decisions for herself and he had many arguments with her about her choices.

When the coroner asked him why he just did not book his wife into surgery, he said that he would have if his wife asked him to.

Mrs Dingle was eventually persuaded to have emergency surgery to remove the tumour, but the cancer had spread and she died two years later.

The inquest continues tomorrow.