Rule 3-421.Interrogatories to parties

Interrogatories are the workhorse of District Court discovery, and Rule 3-421 gives them broad reach. A party can ask about any non-privileged matter relevant to the subject matter of the case — not just the asking party's own claim or defense. It's no objection that the answering party already knows the information, or that the answer itself wouldn't be admissible at trial, as long as it's reasonably calculated to lead to admissible evidence. Interrogatories can also probe the existence and contents of an insurance agreement that might cover a judgment in the case, though disclosing that agreement doesn't make it admissible at trial on its own. And a party can use an interrogatory to request documents: written instruments a claim or defense is founded on, prior statements by the party seeking discovery, and written reports from experts the responding party plans to call at trial — with the court free to bar an undisclosed expert's testimony if that report never shows up.

The rule caps the volume: one set of no more than 15 interrogatories per party, unless the court allows more. Interrogatories that are grouped, combined, or dependent on each other still count separately, and each form interrogatory pulled from the Rules Appendix counts as one. Timing runs off two triggers — the plaintiff has to serve interrogatories within 10 days after the clerk mails the Rule 3-307(d) notice, and the defendant within 10 days after the deadline for filing a notice of intention to defend. A party served with interrogatories has 5 days to move for a protective order on grounds of annoyance, embarrassment, oppression, or undue burden or expense.

Responses are due within 15 days after service, or 5 days after the responding party's notice-of-intention-to-defend deadline, whichever lands later. The response has to answer each interrogatory fully under oath — or state clearly the grounds for refusing — and must be signed by the party. When the answer can be worked out just as easily from the responding party's business records, that party can point the other side to the records instead of writing out an answer. Either party has a duty to supplement a response once further material information turns up before trial. If a response falls short, the discovering party can move to compel within 5 days; if a party skips answering altogether, the court can respond with sanctions ranging from barring certain evidence to entering a default judgment. At trial, answers come in under the ordinary rules of evidence, and if only part of an answer is offered, the other side can insist that any other part be introduced too if fairness calls for it.

An amendment effective October 1, 2026 adds a court-override option to the timing provision in section (b): both the plaintiff's and the defendant's 10-day serve-by windows become subject to a court order setting a different deadline. The 15-interrogatory cap and the underlying 10-day windows tied to the Rule 3-307(d) notice and the notice-of-intention-to-defend deadline still apply by default.