Two horses from the stable of suspended trainer Ben Smith have returned prohibited levels of cobalt from raceday swabs.

Iron Duke and Elaborate tested above the allowable threshold after their wins at Newcastle on August 25 and Wyong on August 26 respectively.

A preliminary analysis of the swabs sparked a stewards inspection of Smith's Newcastle yard last week.

Stewards tested six horses during the inspection and after speaking to Smith, the trainer was stood down.

They found Smith had given false evidence while refusing to give details relating to unlabelled and unidentifiable substances in the stable.

Further out-of-competition samples were taken from Smith-trained horses on Tuesday.

An inquiry will be held once the results of those swabs are known and stewards have completed forensic examination of the confiscated materials.

Stewards are also interviewing "persons of interest" in the investigation.

Smith has risen to prominence over the past 18 months as the trainer of Group One winners In Her Time and El Dorado Dreaming.

In Her Time won the Group One Galaxy and El Dorado Dreaming claimed the Group One ATC Sires' Produce Stakes during this year's Sydney autumn carnival.

On the strength of her Galaxy win, In Her Time was snapped up for a slot in next month's $13 million Everest field.

Along with El Dorado Dreaming, In Her Time has in the past week been transferred to fellow Newcastle trainer Kris Lees.

They have both been cleared for racing after producing clean samples and they had their first public appearance for Lees on Wednesday.

In a 1000m barrier trial at Newcastle, El Dorado Dreaming narrowly beat her older stablemate.

While Lees said In Her Time would have an Everest lead-up run in the Group Two Premiere Stakes at Randwick on Saturday week, he was unsure on a spring starting point for El Dorado Dreaming.