A reagent kit (10; 110), comprising: - a reagent container assembly (15; 115) with at least one reagent container (12; 112) for accommodating a substance, the reagent container (12; 112) including at least one container body (13; 113) and at least one closure (14; 114) which is associated with the container body (13; 113) and which is mountable or provided thereon, wherein the closure (14; 114) comprises a closure base member (16; 116) and a lid (18; 118) supported movably on the closure base member (16; 116) for movement at least between a closed lid position and another lid position, as well as - an in-transit securing means (66; 166) which is mountable or mounted on the reagent container assembly (15; 115) in a locking position and which, when mounted on the reagent container assembly (15; 115), is movable relative to the reagent container assembly (15; 115) from the locking position into a release position, wherein, in the locking position, the in-transit securing means (66; 166) secures the lid (18; 118) in the closed lid position, and wherein the in-transit securing means (66; 166) is removable from the reagent container assembly (15; 115) out of the release position, characterised in that the lid (18; 118) is pivotally mounted on the closure base member (16; 116) for pivotal movement about a lid axis (18a; 118a); wherein by moving the in-transit securing means (66; 166) relative to the reagent container assembly (15; 115) from the locking position into the release position, the lid (18; 118) is moved from the closed lid position into the other lid position, and wherein the in-transit securing means (66; 166) can be moved by sliding displacement relative to the reagent container assembly (15; 115) in an unlocking direction from the locking position into the release position, wherein the in-transit securing means (66; 166) comprises at least one ramp-shaped engagement element (94; 194) and the lid (18; 118) comprises at least one mating element (56; 156) co-operating with the engagement element (94; 194) in such a way that, upon sliding displacement of the in-transit securing means (66; 166) mounted on the reagent container assembly (15; 115) from the locking position in the unlocking direction, the engagement element (94; 194) and the mating element (56; 156) are in mutual sliding abutment engagement or come into mutual sliding abutment engagement, so that, by sliding displacement of the in-transit securing means (66; 166) in the unlocking direction into the release position, the lid (18; 118) can be moved from the closed lid position into the other lid position. - a reagent container assembly (15; 115) with at least one reagent container (12; 112) for accommodating a substance, the reagent container (12; 112) including at least one container body (13; 113) and at least one closure (14; 114) which is associated with the container body (13; 113) and which is mountable or provided thereon, wherein the closure (14; 114) comprises a closure base member (16; 116) and a lid (18; 118) supported movably on the closure base member (16; 116) for movement at least between a closed lid position and another lid position, as well as - an in-transit securing means (66; 166) which is mountable or mounted on the reagent container assembly (15; 115) in a locking position and which, when mounted on the reagent container assembly (15; 115), is movable relative to the reagent container assembly (15; 115) from the locking position into a release position, wherein, in the locking position, the in-transit securing means (66; 166) secures the lid (18; 118) in the closed lid position, and wherein the in-transit securing means (66; 166) is removable from the reagent container assembly (15; 115) out of the release position,