The units were shut down last month so staff could help cover A&E at Hereford County Hospital.
Today (Monday), Wye Valley NHS Trust (WVT) confirmed that the units are open again.
As reported by the Hereford Times, the future for both faces review with their attendances falling to as few as five patients a day.
The WVT board has been told that the need for this review is "increasingly urgent" as low patient numbers make the units too costly to operate.
But WVT currently has a contractual obligation to provide them.
Both units have already had their hours cut and were shut as recently as January to ease the pressure on A&E
A&E at Hereford can see as many as 180 patients a day - despite being built to take a daily maximum of 125.
From today, the MIU at Leominster Community Hospital will re-open from 8.30am to 5.30pm Monday-Friday, while the MIU at Ross Community Hospital will open between 8.30am and 5.30pm on Tuesdays, Wednesdays and Thursdays.
Neil Doverty, WVT chief operating officer, said these hours allowed the Trust scope to run a "safe and efficient" MIU service from the two hospitals while continuing to manage pressures in A&E.
“The decision to temporarily close the MIUs allowed us to make the best use of our staff. We’ve been experiencing unprecedented demand for our A&E service for this time of the year and I’d like to pay tribute to my colleagues across the Trust who have been working tirelessly to respond to this challenge," he said.